1. Unfortunately this is not possible. The server does not detect in-game stuff. The server is only used for matchmaking and connecting the players to eachother and was no way to "watch" a match. There is a tool that already detects some kind of cheats (for example, the "Instant drift"-cheat), but this tool has to run on a player's computer and must have access to the Wii's internet traffic: mkw-ana.
2. Only thing I can say for optimal connections: Make port forwardings for UDP 1024-65535 and TCP 28910, 29900, 29901.
If you get disconnected in the race, this has absolutely nothing to do with the server. As soon as you are in a room (friend room) or seeing the other players in live view (global), the server has no influence on your connection. When you disconnect, either you or one of the other players had a bad connection.
3. Currently in development. Will be enabled somewhen in the future.

Bean said the NATNEG server would cause a lot of lag as it doesn't work as well as the original one. Or to be more specific, because of how it works worse, many more players use the host as a proxy which creates lag especially in worldwides and if the host's connection isn't very strong. Atleast this is what I understood.

Is the NATNEG considered finished? ALTWFC's NATNEG works much better afaik.

The decision to use someone as a proxy (this is not always the host) is done by the clients (during race, when NATNEG is finished) if they recognize their own connection is too bad. NATNEG does not decide if someone uses someone else as proxy.

I do not see any differences between Wiimmfi-NN and altwfc-NN. Both need the same time (~ 6 seconds) as Nintendo to match up two players.
The 6 seconds delay is caused by the game and are not a problem of the server.
A natneg server can not work "good" or "bad", it can only work "slow" or "fast" - it only receives two packets from two players with the same ID, and sends the packet from player 1 to player 2 and the one from player 2 to player 1.

How do you even see if someone uses a proxy? Are you using mkw-ana?
I checked a few of my dumps of global races, and in most races, noone uses a proxy. I a few races, one or two players are using a proxy. This was the same at Nintendos servers - proxying is used if a client does not have enough upload speed to send the data to the other clients.

And yes, NATNEG is considered finished.

I might aswell forward this question to @MrBean35000vr as I just repeated what I understood from a chat I had with him some days ago. Watching a twitch stream, players were talking about lag and I said the server has nothing to do with ingame lag as it's only for matchmaking, but Bean said NATNEG would be the problem why Wiimmfi has more lagging players and that ALTWFC would have a better NATNEG working for more players - if I recall that correctly.

NAT Negotiations has always been an issue with Wiimmfi, but I don't think we've found the actual cause for why its function becomes a hindrance in larger rooms. It should be noted that while Nintendo WFC asks for players to have ports open to the Wii, its games seldom actually require this functionality to work correctly, and that makes sense; that's why natneg exists to hole punch the router. With that in mind, here are some scenarios that Wiimmfi handles worse than WFC from just experience:

• Having a bunch of people join one room in succession makes natneg effectively ddos'es the host for some reason, WFC doesn't experience anything quite as bad as what Wiimmfi can do to hosts. altwfc, while more stable, has not yet had a full on host stress test; the largest increment I ever had at one time was 2 to 5.
  
• The good host vs bad host scenario. Wiimmfi has a problem with some routers or repeater type setups that hinder host compatibility. Meanwhile, WFC's bad host are attributed mainly to an unstable internet connection. Bandwidth and ping-wise, it does not appear like MKW player internet connections have worsened from WFC to Wiimmfi, quite the opposite actually. You could also note here that altwfc does not have the same router/repeater incompatibility that Wiimmfi has, for some reason.