Add up the total Amps that will be pulling if everything you have connected is switched on the get a cable to suit. Cheapest option will be to go and buy an Amplifier Wirng Kit and use the Power Cable from that. Will get a cheap one for 10-15 £
Either but thinwall is much easier to work with. Remember the fuse must be the weak link not the cable so if your`re not sure just get the highest amp you can. 30 will cover all of what you are doing.
What size tyres do you want to fit? can tell you what lift you need then. I`ve got 4" suspension and 2" body with 35" (36.5 :) Tyres ) which is about right