I would suggest not limiting 5 people to be able to train at a time. It will stay in control of just a few people whom switch between other chars or friends only. Have a trainer in an open room whom 8 Knights + 20 Paladins can attack and a few of them. As long as they are in a room they should be fine.
As far as donations, a knight set should be the best items to purchase, that is reasonable enough for anybody to need if they want started eq. Price it kind of expensive so they will only buy if necessary, and they do not cost a lot from djinn so if they were to buy a bunch it's a waste of real cash. Knight arm/legs be about 1$ usd each while 1 month premium is 3-5 usd. It will not destroy economy and if they 'need' gear they have average gear available.
As far as weapons I would only offer fire sword, knight axe, skull staff for Knights, and wand of inferno for mages.