I'm not the most experienced in this area, but I can offer a little input- I bred my WBxTB mare last spring and was in a similar predicament lol This might be bit of an info dump sorry!
1. My advice if you're going to go AI is used the best, most experienced vet you can- whether that is at the facility or a vet who can come to you. Timing is extremely important with AI, as you don't usually tease them and chilled/frozen doesn't have as long a life span when compared to fresh. It might be worth inquiring at the facility and see what their prices are like, whether your mare would need to stay there, is it a bulk fee or if she needs extra drugs is there an add on, ect. Or if she is a stressy mare, it might be better to keep her at home, in which case start looking for a good repro vet with a high success rate.
2. With AI vs live cover, it can be bit of a gamble. With live cover, they do get a bigger 'dose' and you can often get multiple covers per cycle, but it does have some extra risks in terms of injury plus, you'll have to haul the mare to and from the stud; whether you leave her there until she's confirmed in foal or bring her home and have her checked there. AI can be more fickle as you really have to track the mare and try to inseminate her just before she ovulates for the best chance she catches. Maidens are bit of a loose cannon regardless, as they've got no previous breeding history. Some people swear by live cover for the first time, others say it makes no difference if you've got a good vet. I've seen maidens get in foal with frozen first go, so it is definitely possible. Are you planning on chilled or frozen? Frozen does tend to cause a more extreme inflammatory response in the mare, so if you suspect she may have some fluid clearance issues it would probably be better to go with chilled. Plus, some stallions just don't freeze well and the progressive motility of the straws can be quite low.
3. I would definitely get a pre-breeding exam done, they can be invaluable if there is an issue. The usual process (at least over here in Aus) is the vet giving a quick physical exam, inspect the vulva conformation of the mare to ensure it is adequate or if she may require a caslick or if she is pooling urine, then they will ultrasound her reproductive tract. This is so they can see if she is 'wind-sucking' or drawing in air, has any fluid present, make sure everything is normal in appearance and to map out the location of any cysts which is important for later on when preg checking her. If she is cycling, they will also looking to see if the cycle and follicle growth is normal. Some vets will do a culture and/or a biopsy on the mare, but some are inclined to not do that on the maiden mares. Its up to you, its not super common practice to do that over here unless the mare has an issue or the stallion owner requires a clean culture/biopsy in the contract. I worked with two vets, one for the pre-breeding exam and another when I actually sent her off to stud. Both agreed that the culture/biopsy isn't really needed unless she goes on to have issues once we start breeding her, but your vet may be of a different opinion.
4. From what I've been told, their nutritional requirements don't actually increase at all until the last 3 months. The foal grows relatively slowly until the last 3 months, so that's when you would start to supplement her diet. Any good quality stud/broodmare feed should do the trick. The feeds designed for broodmares are usually much more nutritionally dense than those designed for riding horses. Obviously, if she starts to drop off or loose condition before then, start bumping her feed up.
Points 5-7 I am not familiar with any of the AQHA or APHA rules but I'm sure other members will be able to chip in! Does the stallion offer a live foal guarantee? If he does I would take that option as breeding can be a gamble and there are a million and one things that can go wrong between breeding and getting that foal on the ground. It can be good to have that little bit of insurance.
The only other advice I can think to give is expect the unexpected and find yourself a good mentor if you can! I had a lot of help from the previous owner of my mare in stallion selection and general tips and tricks and my uncle (who has been breeding and racing stbs for years so knows just about every trick in the book lol). Had all my pre-breeding checks done early, at the tail end of winter so I could send her up to my uncle's at the start of September. She's bit of a stress-head, so I wanted to have as much time as possible for her to settle. Stressed mares are typically harder to get in foal. I was really lucky with my vet, as he would charge a 'base rate' for the season, so I could pretty much tick that off before we'd even started. The next thing to keep in mind is your stallion; and by that I mean what days do they collect/ship, what the collection fee is, do they require the shipping container back if so within what time frame, how much warning do they need before collection and how are you getting the semen from A to B. It is really important to keep your stallion owners in the loop about what's happening with your mare. I nearly missed out once because the stallion wasn't able to collect the day we needed him, which then means you have to wait until the next cycle. The shipping fee can add up quite quickly too, depending on how far it has to travel and what kind of transport you go with. If the stallion is close by, it might be cheaper to just pick it up yourself. That's what I ended up doing as the shipping itself was going to be $338 each time, plus the collection fee which was also $300. So if you've got to do multiple cycles it can added up reeaallllyyy quickly. My mare took three cycles to catch, so I'd spent over $900 dollars just getting the semen from A to B, not including the stud fee or the vet fees on the mares end.
Getting your mare scanned is really important too, one to confirm she is in-foal and the next to make sure growth is normal and there's no twins. An experienced vet should be able to pick up an embryo about 14 days after breeding, then check again two weeks later to make sure its stuck around and then again at 30+ days to check for a heart beat :) Like I said earlier, my mare ended up taking 3 goes to catch. Well when she did catch, she caught with twins! So one was pinched off, but the vet noticed a suspicious looking shadow. He was coming back to check her again in two days anyway to make sure she didn't loose the remaining twin and again check the shadow. Well, when he came back that little shadow had developed into embryo number 3. It was much smaller than the other remaining embryo so it had obviously been fertilized a few days after the first two. Another reason why keeping tabs on how many follicles your mare has before inseminating is useful, can give you a bit of a heads up if you need to look for twins or not. Anyway, that one was also pinched and vet gave my mare a few drugs to try and limit the inflammation and then fingers crossed the other one was still around at the next check. Luckily it was, though I swear this mare is trying to give me a heart attack with all the crap she threw at us lol But we were lucky we scanned her as often as we did or we might have missed that 'triplet' and by the time we noticed it at the 30+ day check it would have been much harder to pinch off and it would have been much more likely to loose both and be back at square one.
Hopefully you will have better luck than I did and your breeding experience is much less stressful! Sorry for the massive wall of text and I don't blame you if you don't read all of it lol Its a very in-depth topic which I am sure you could discuss indefinitely! Wishing you the best of luck for a ripper foal!