Before I start I want to say there are alot of servers out there and alot of donation sites so you will have to make yours uniqe.

Ok so where to start well what I always start of with is the site you can get a great donation site for free such as Buycraft or you can use enjins built in store which I personly use both of these sites are great easy to setup and can be used for free but the paid features offer so much more.

Perks:
Personally I think some servers go over the top with perks like giving them very OverPowerd kits or items but these perks can be just as useful and give less of an advantage.

A coloured tag can make all the difference because it shows players that the person has donated and it can also help other people to donate.

A reserved slot so when the server is full they can still connect I only recomend this if your server gets full.

If your server is survival access to set more then one home will help alot.

/hat just something for fun

Maybe give them access to apply for staff since they are less likley to pay then abuse powers.

/enderchest have a portable enderchest

/workbench for a portable crafing table.

I will add more if you are interested how I have my website and store setup goto rndgaming.net