The context that was given is 100% disallowed by the EULA
"You are allowed to sell in-game items so long as they don’t affect gameplay
We don’t mind you selling items in game, but they must be purely
cosmetic. Pets, hats, and particle effects are OK, but swords,
invincibility potions, and man-eating pigs are not. We want all players
to be presented with the same gameplay features, whether they decide to
pay or not."
As programmers, we can make any item have any function. 
All I meant is that we can turn just about any item in-game into a cosmetic feature. Blocks which, when held, give you a particular trail, for instance, rather than just having a trail at all-times. That block couldn’t be used in any advantageous way besides giving you a trail effect.
EULA or not, prices should probably remain below 50$ In the case of subscription ranks you could give the option for a more expensive one time payment.
I should’ve been a bit more specific on that:
-i meant access to blocks by donation. As blocks are gameplay elements → breaks EULA
-access to waepons may be fine, if theres a freely available weapon with the same function and strengh
-visual stuff while holding something is ofc fine
I totally agree to that.
I would never play on a server that breaks the EULA by selling ingame-money, points, classes, items, dungeon-accesses or something like that. I’m always willing to donate, but those who do that to get items are no donators. They are purchasers. In addition, I’m not sure whether the loss of a so called “donator”-rank after one month breaks the EULA. Even though it does not exactly forbid that as far as I know, it does not match to the gist that is to prevent monetization.
The best way to handle it is to give donators a chat and nameplate title and some little fun things - without taking it away.
How much they should have to donate? I agree that it should not be more than the game’s price. 10 USD is enough.
The best option for donator ranks are subscription based with a one time pay option. This way you can focus on keeping the players you have rather than getting new players onto your server(Although not a bad thing.)
The way I have set it up on servers in the past is allowing payments for pets, hats, nicknames, and renaming items for the death messages. One donator tier and thats it. Also, if you play on the server for 50 hours you gain the same permissions as a donator. Donation requirement is $10, anything higher is accepted if you just want to help the server out.
I have gotten many donators in the past and no-one has complained of unfairness as of yet.
I have 5. The first two are extremely cheap ($3, $5 respectively) I think anywhere from 0-5 is okay, 5 being a bit high. The first two can be gotten through voting/being loyal to the server and contain mostly just convenience stuff, such as /workbench /enderchest etc (about 20 apiece), contains some fun stuff as well and all donator rewards contain a kit. The next two are slightly more fun geared with a few more commands apiece, still relatively cheap ($10, $20) These get slightly into the OP/pay to win scenario, although any pay to win features are disabled in the PvP survival world. Last one is $30 and contains stuff like gamemode, again disabled on the PvP side.
I personally only do lifetime, but if I ever did subscription I’d recommend it for a reoccuring kit or something like that, and at a fairly cheap price ($5~)
Varies for me, I’ve had them cost up to $45 with people paying for it in the most active times of my server, when I need money, I take advantage of something I like to call “The Steam Sale Syndrome”. Where I just discount everything up to 75% off, I even tell playersto wait/ refund their money if they donated a few days before I do this
Most of my current player base have donated in one way or another, I don’t try to make money off of them by any means, I feel what I have is enough to cover my server costs, and most of the time I’m covering the last $20 or so. I really think this last part is up to you, really charge whatever you need to keep the server running, keep information easily available (IE: tell your players the server costs, tell them how much money you have dedicated to the next months payment). I think I have a pretty good relationship with my players, my server is by no means large, but it usually pays for itself, and the few times it hadn’t within a few days of it going down I’ve had players contacting me asking me if they could donate to help out.
Really if you’re trying to keep your server afloat, don’t worry about the donations, worry about getting to know your players and making friends, the rest will follow.