Yeah I think there's a code for new players which give you GC on starting out.
What's your highest tier atm? ŰberTech points are less worthwhile the higher up the tiers you are, as you can only get 11 ŰberTech points with that 100 GC, and most cubes require more than 11 tech points to pick up. (1 Tech point of any tier + 9 GC = 1 ŰberTech point; also
Über Points and Tech Points cannot be mixed when purchasing technology).
Walker legs let you go pretty much everywhere, but have the massive drawback of being hard to protect effectively.
You can definitely have multiple rail guns, but rails suffer from having the longest reload period in the game. Reloading before firing all your rails reduces this. Rails also require you to have a very patient playstyle, and have very particular quirks which take a while to get used to.
Plasma is currently a grenade launcher which tends to favour hit and fade tactics. If you're curious about damage models for plasma, I've explained some of them in my previous posts.
(also plasma is OP)Electroplates are essentially regenerating shields. They are better against burst damage because you can hide and let the shield regen, but not as good against sustained fire which can break the electroplate once the blue shield is down.
EDIT: The one thing that I'd recommend getting with the starting GC is better armour cubes (which you can actually afford with that 100 GC
)