Itinerary for Laos

In january 2008 I will be travelling in Laos for about 4 weeks (after one month in Thailand). After Laos I will also visit Cambodia and Vietnam (maybe good to know if you want to give me some advice). I am a quite experienced traveller but it’s my first time in SE Asia so it’s always good to get some good and actual advice. I don’t care about luxury (and prefer atmosphere above that): a private, clean and basic room (with fan) will be fine for me.
Here’s my global itinerary for Laos:
Entering Laos in Huay Xai (day 1), to Luang Nam Tha by road (2), Muang Sing incl. trekking (3-4-5-6), Luang Nam Tha (7), Udomxai (8), Luang Prabang (9-10-11-12), Phonsavan/Plain of Jars (13-14), Vang Vieng (15-16), Vientiane (17-18), Savannakhet (19), Pakse (20), Bolaven Plateau (21-22-23), Champasak (24), Si Phan Don staying on Don Det/Don Khon (25-26-27-28), leaving Laos for Cambodia (Stung Treng).
Some questions about my itinerary (detailled questions will follow later):
1. Wanna do at least one trekking in Laos, is Muang Sing the best place for this? Or are there better options in/around places like Luang Nham Tha, Vieng Puhka, Muang Ngoi or Luang Prabang.
2. Is there a scenic boat route to insert in this itinerary (I suppose it will be dry season)?
4. The route is logical? I know the places are more or less standard but are there any places which I should insert or maybe skip?

Thanks in advance for you answers,

Harry.