I agree with everything you pointed out except the 50 move rules.
Since there are potentially more than 2 players in an endgame, its natural to have a 100 move rule instead of a 50 moves rule. Because if 4 players are still in the game, 2 of them being ahead in points but with lonely kings, and the other having 2 bishops for instance, he will need more moves to mate the 2 remaining kings. besides, 2 players making 50 moves is like 4 players making 100 moves. So I think the 100 move rule is a good idea.
Aside from that, as I said previously, I think everything you pointed out is correct. the 5 move repetion seems irrelevent, 3 times like normal chess seems fine to me. Also, I think it's natural for any position that would be a draw in real chess to be worth 10 points, wether it ends the game or not. A win is worth 1 point and a draw is worth 0.5 points in real chess, so in 4 player chess, if a mate is 20 points, a draw should be 10 points. It seems to me like the most natural way to do.
( I believe the rule is 100 move in total and not 100 moves per player? So if the rule is 100 per player, you can forget about what I said about that)
I think this is a minor issue, but I think there are inconsistencies with the point system when it comes to positions that are drawn in classical chess.
Insufficient material (only kings left): 0 points for each player
50 move rule (or 100 ply rule to be exact): 10 points for each remaining player
5 move repetition: 10 points for each remaining player
Stalemate: 10 points to each remaining player except the stalemated player.
Please correct me if I got any of the rules above incorrect, but I believe these are the current rules.
I think all drawn positions should have the same rules, so what I suggest is to always give 10 points to all remaining players (including the stalemated player). Of course stalemate can be seen as an exception since it does not end the game if there are other players remaining, but since it is a draw in classical chess it makes sense to me that the player that gets stalemated should get some points.
Also some other minor things I would change is from a 100 ply rule to a 50 move rule and change the 5 move repetition to a 3 move repetition. Those are the limits to claim draw and not for automatic draws in chess (automatic draw/declared by arbiter is 75 move rule and 5 move repetition). I can see merits to using either the claim limit or automatic limit though.