Hello from Sunny Aberystwyth Mid Wales confused about building a 8x4 router

Hello and here goes!!
I'm looking to get into either buying or building an 8 x 4 router, have been lurking and reading this forum for past few weeks and decided it's about time I introduced myself so I can start asking questions and hopefully getting the advice I need about what to do.
I'm hopefully looking to build a machine to work on 8 x 4 sheets of ply, MDF and Laminated chipboard upto about 25mm thick I guess although I'd not really want to limit myself to that, hopefully capable of handling ally sheet and would it be too far fetched to possibly make it possible to remove the router head and attach a plasma head to make a really versatile machine.....not for great thick steel more thin sheet maybe 2 or 3mm? or is that too far fetched?
I'm a carpenter and joiner who likes to dable with most things and class myself as pretty competent with most things and trades, steel cutting and welding is not a problem for me.......electrics on the other hand are my greatest downfall although my father is a retired TV engineer so hopefully that should go in my favour!!
.......I'll pop over to the router section and ask for advice now I've introduced myself.

Steve