[Nijnrich]

I totally agree with your complaints about lack of realism. However...

As gameplay is concerned, the amount of weapons is an issue if playing with a undefined number of players.

Supposedly you want to set a sort of limit (in percentage) for all weapontypes. The only way then to get a new weapon if the overall balance is within the set limits. Thus implicating that joining for a new player will automatically give a restriction on the possible weapon selection which is just temporary based of the number of weapons of that time.

How to count the number of useed weapons .
Weapons in hand by player, (cheat coming up by throwing away weapon before teammember with RW joins) or maybe counting the weapons started by all the players .

What to do in objective mode type games. Have a long weapon count and fiddle around until finally somebody out of generosity gives up his Stg44 for a G43??

Not to mention the ability to switch weapons during TDM and following problems.
Bottom line
If you're that keen on fighting the historical way, try to make a new set of clan fighting rules. Clan fights are usually by the rules so why make complicated scripting..

Then make your own mod. Set the ammo low for the odd weapons. That will automatically let people choose a more normal weapon , remove the shotty and RL's and then MOH will be a lot more fun and realistic.

Changing the weapon choice itself will definitely lead to too much restrictions and will ruin the game.