Arena Size

Ok so I didnt know where to post this so I decided since I do mostly western riding whats a good size arena for a general horse boarding traing and lesson facility? We are moving to 5 acres where I have my own 7 stall barn 2 tack rooms lights for an arena and No fencing yet. Whats a good general size arena I don't want more than an acre in size but an acre is a bit much for the area im given to work with. Also what size round pen is a good size and how many panels would I need to make it. Lol we dabble in every area of riding??? Please help!!!!

Well I learned to ride in 70x200 foot arena but personally I would go with 80x150 (feet).
I love big arenas but I have learned if you can ride well in a small arena you will do even better in a bigger one.

My arena is 100'x100' and I think it's too small. I wish it were 100'x150'. Most round pens that I have worked in were 50-60' across. That size seems to be about standard, but I have no clue how many panels you'd need. Depends on how big they are.