So, I wouldn't recommend riding in a field with other horses on a regular basis. You don't know what could happen, it could be a potential safety hazard. I'm not trying to sound sassy in any way... I mean, you could ride in and nothing could happen. I would just rather assess the added risk than sugarcoat it, you get what I'm saying?
I have ridden in a field with other horses before but only for a short amount of time because walking through that field led to the trail. I did ride through that field numerous times and on a regular basis, but only for a couple of minutes to get through that gate.
Make sure that electric fencing is not electric if you do decide to put a horse near there. I'm not familiar with that kind of fencing, I prefer wood post/rail fencing that is good ol' fashioned and sturdy.
Some people do very well riding in fields, but my old stable did not have an arena so my arena was a small grass ring. It was uneven and eventually became a safety hazard for my training. It's also that kind of thing that depends on what you are actually doing and what you are trying to achieve in that ring, your horse's training, your experience, how the footing is and the elevations, etc.
There are several things that go into it. If you could post pictures of the area that could help some people give you more accurate advice. However, if you ask a trainer or someone more experienced that can actually view the area in person, they may be able to help you determine what to do based on your various situation.
I understand that sometimes there is not access to more ideal riding space. I admire that you are trying your best to work with what you have. I'm not completely educated on the matter, so like I said, I suggest getting more opinions. However, I figured I would offer mine. (:
Thank you for your time and happy riding!
God bless, englishaqh (: