if you want to disconnect ALL power just pull all the leads off both batteries, if you leave one still connected it will still be powered as if both were still connected. it doesnt matter what order you do it in. oh and welcome
+1 on gunning's reply. The negative comes off first as it can inadvertently touch the body with the other battery still fully hooked up without shorting. Once both negatives are off, the positives can touch the body with the engine off and won't short.
I had it for just over a month. There is a few on the list... Definetly a 2" suspension lift first, upgrade to 32" tyres, fit a snorkle, possibly a stero upgrade in there somewhere too.