You should really enjoy your Mercedes as a project.

Since you really do not know how many miles it has on it I would put the timing chain and stuff that touches it at the top of the list....if a broken chain , due to a rail or guide giving way ( since they seldom break by themselves ) causes piston and valve damage your enthusiasm for the rest of the stuff will be affected adversely. That is my understatement for the day. Having the timing which is controlled by the chain set properly is very important to how the engine runs.

I would not use anything at the same time as the Diesel Purge unless it is suggested on the side of the can.

I would put "Methanol/ H2O injection" at the bottom of the list.

I would suggest that the first special tool you make is the one shown in the FSM for bolting above the cam gear when changing out timing chains which keeps the chain in contact with the cam gear when rolling in the new chain. Then offer it up to the ' borrowing tools ' section after you have used it.

Always take lots of digital pictures of your projects so you can share them with the forum...
Good Luck and welcome to the forum.
Greg