Very happy with my system, I have go van ports, but to be honest unless you have are going to plug your reels into them rather than leaving them in the van they aren't necessary, but I suppose they are handy for filling the van if security is an issue and you wan the van locked.
With regards the tank, there isn't much difference in the prices, so just get as big a tank as your van will take, what van have you got?
We have a 650l 2 man set up so a minimum would be 300L
Get the split relay charger, that's handy, also don't bother with their poles, get yourself an clx or slx if you can afford it.