Q's on Cycling Laos in June/July

Hello,
My boyfriend and I are planning to cycle from Vientiane to Luang Prabang in late June/early July this year. I know it will be the rainy season, and it's going to be hot (I know I know), but it's the only time we can go before starting new jobs, and we're just too stubborn not to at least try to cycle part of our trip. I have a few questions:

• We're planning to buy bikes in Vientiane. The bikes we have at home are road bikes, and I gather aren't going to be worth anything in Laos in July, and it would be a hassle to transport them anyway. I know there are some bike shops in Vientiane, and although a touring bike would be more our "style," we're thinking we may need a mountain bike for this trip. It's my impression that the roads will be rough, mostly unpaved, could be some washouts, etc… Anyone have any input on this? Also are decent-ish bikes available at the shops in Vientiane? We don't want to spend a fortune of course, but would like a step or two above a Chinese clunker.

• We've got a GT Rider map on the way, and haven't planned our exact route yet. Any tips on what route might be best this time of year?

• Any other tips on cycling Vientiane to LP in July? :-)

• There's a possibility we will get a second wind after arriving in LP and decide to hang onto our bikes as we travel into Thailand. We're planning on taking the slow boat to Chiang Mai, and it sounds like bringing the bikes on board won't be a problem. So, I suppose I don't really have a question here, but advice from anyone who has done this would be greatly appreciated.

Thanks all!
Loganator and Hippie Dave