Yes, you can remove the network card, but why go 10 MBit when you can go 100 MBit? I have experienced that some PCMCIA ethernet cards slows down my machine.
You might be lucky to get the Voodoo5 working, but on my system I can't use my (also brandnew out of the box) Voodoo4 4500, but I can in my Mediator for my A4k.
I don't know for sure if there is anything speaking against using 2 gfx cards in Mediator, but some ENV settings are set to config memsize of the GFX card and type of Voodoo card used. Try it out with 2 GFX boards when you get it, but don't get your hopes up. Get a switch for the computer and you only need one monitor
