First things first congratulation for your successes
What you have there is a clan omni mech. So you can buy whatever variant you want (you of course shouldn´t buy a variant you already have

). The rest can be exchanged. You could for example exchange the left arms of your prime and the new one to have an energy slot more there. Or you could get an shc-b left torso to use ECM with it. It is totally up to you! For saving money it wouldn´t be the worst idea to exchange parts, if the ballistics arent so good for you after all
As for the gauss: Yes, the weapon can explode. For other ballistics it is the ammunition that explodes. So not such a big problem, especially if you think of the C.A.S.E. in clan mechs. The gauss is a very good long range weapon. 1 Heat, 15 Damage ... but the firing is something you need to getting used to. Then there is the cooldown, which is kinda long. But hey, that´s what backup weapons are for
The machine guns are a short range mech killer. You probably know that. There is no infantery, so I don´t rate them as self-defence. They are used mostly the same way on all mechs. If there is no armor, they are great for crits. If there is ... the strip it away in really really small chunks.
You could use UACs instead of machine guns and gauss, for example. Or you could exchange an arm and get an energy weapon as backup.
As for your money: For refitting purposes it might be an idea to keep some money ... but to be honest ... you have everything you need after buying the new mech to just exchange parts, if you run low. Perhaps kepp around 80k for your consumables. But even that you have easily after one game.
Edit: What Rogue Jedi said!
As for Faction Play ...
Wait for the patch

After the changes there, you could need less mechs or so ... who knows. At the moment you should have a few mechs of your own, fully outfittet. So that you don´t have too many trials in your dropdeck (4 mechs, 160 to 260 tons of tonnage between all of them). As for the skill level ... depends ... if you are comfortable with your targeting and other skills, you should be ready. If you are a teamplayer ... even better. Solo runs are seldom effective in FP.
But all those things ... might change at the 19.04.2016. So wait for the patch for FP
Edited by Ibrandul Mike, 18 April 2016 - 12:11 AM.