Im using miniature horse feed pellets hay and letting him eat a little on grass my mini acts like he is starving when he gets on grass but im feeding like I should be and the biting! That's a whole other story lol
I suggest enlisting the assistance and direction of a good trainer and finding a mentor (or two or three). Your little one is at a critical point where the need for good direction and training is paramount. It is vital that a young horse be properly brought up and many a potentially good horse is quickly ruined by well-intentioned, but unknowledgable, individuals.
If I were you I would be asking the vet, or a person who KNOWS ALOT about horsese, and has one not just loves them. Good luck with your mini... DO NOT tolerate biting.. if he is biting slap him on the rump.. if not he will think it is ok and will consider himself as boss.. you may also want to ask about proper care for diets, farrier, teeth floating, etc.
I may be in the minority with this and I certainly don't mean to offend anyone but owning an 8 month old horse - mini or otherwise - is absolutely the wrong thing to do as a first attempt at ownership.
You can get a lot of good advice here but knowing how to put it into practice and to what extent takes experience and understanding. An 8 month old is very impressionable and handling him/her the wrong way (yes I know you are asking for advice) will create a lasting habit with this horse that may ultimately make her unsellable or unhandleable in the very near future.
My opinion is to get her to a more knowledgeable owner and, if you are determined to own a horse, start by working with someone who knows how to teach you.
It is 100% wrong and unfair to make an 8 month old horse your learning project.
My horse has been checked by a 30 years horse vet. He is in perfect condition. I chose to get the horse because I have always loved horses but wasnt able to give one a good home, now I am. I do plan to send my horse to a trainer when he is older, but for now he is in good care. I just wanted advice from this forum because I am new and my vet said horses are a lifelong learning experience not something just anyone knows about these days. I have talked to breeders all over before I put all my money and soul into this.