This is the way horses are: your horse is the "new kid", the lowest in the pasture's pecking order. The gender make up of the pasture has an effect too, as does the gender of your horse; but they will all eventually work it out, it's a natural part of their world and they know how to handle it.
Violently rejected
A horse pasture should have enough space to graze as well as space to run. One horse is 1.5 AUs, so depending on your locality, pasture quality, time of year, etc., you could pasture one horse per 2 acres or more per month.
In a stable in the countryside?
A horse in a good pasture will do.
This can depend on the breed of horse and type of work the horse is being used for. Example, is the horse kept for training and competition or is the horse for hacking/riding for pleasure. Stable vs pasture can also depend on the time of year -winter vs summer and of course the quality of the pasture- is there shelter and food.
Yes and no. Yes for if it cribs alot and if its in a small pasture. No for if its in a big pasture and if it doesn't crib alot.
Yes
It is good for a horse to have another horse due to swatting the flies, and just for the company in the pasture.
No. Pasture the horse on untreated grass. No treatment of any kind, except cutting the grass with a lawn mower.
It can help so long as the horse doesn't have what's called 'pasture heaves' where it's allergic to the molds in the grass.
No if you put a ligh layer over the pasture then no, this is actually extremly benificial to the grass (for horse manure is great fertilizer).
There would be a total of 2006 legs in the pasture. There are 500 cows with four legs each which is 2000. The horse has four legs and the farmer has two legs. This makes a total of 2006 legs.