Visas and border crossings forum

Hi All!
Im off in 8 weeks for a 6 month trip, well be in SE Asia for 13 weeks and doing a big loop, starting in Bangkok up to Northern Thailand, Laos, Nothern Vietnam down to Southern Vietnam, then across Cambodia and back to Bangkok to do the islands and Malaysia.

My question is where is the best place to leave and enter each county on this route. It seems Huay Xai from Thailand to Laos makes most sense then mabe at Hue but wanted to go to Sapa so would this means lots of pointless backtracking?
Also where and when would be best to get visas, i was thinking chang mai for laos one or on arrival, luang prabang for vietnam one then dont know for cambodia! also i have read so many conflicting stories about thai visas, am i right in thinking i will need the tourist one for £28 as i dont have an onward flight out of thailand? and just 30 day on arrival when we arrive from cambodia?
sorry for the billion questions, i will be very grateful for any advice though! Thanks, Lx