I am doing this route at the moment ( returning ) here are some suggestions.
day 1 - malay border to petchaburi ( I think, pushing it I could make Nakhon Patom or somewhere past Bangkok. I know Malaysians can push hard! So maybe easy for you.
day 2 - easy day - to surin - I stayed in a pretty decent and cheap hotel, I will check my GPS and post in the accomadation section.
day 3 - surin > border .. It took about 2 hours to clear Thai and laos customs. Expect to pay silly amounts several times and wait too long for paperwork to be completed.
The Thai side was great, efficient, helpful and friendly .. Laos, not so, just speaking Laos to you expecting to understand completely.
I didn't like this attitude in Laos, some people were great, but others spend all day watching Thai dramas and news on TV then had difficulty in reaching a common language to communicate with.
1.100b at Thai immigration
2.25b at customs
3.40b for some guy to write your name in a book in Laos.
4.200b for laos customs
then finally stamp the papers at the checkpoint.
border > pakse for an easy lunch and change money.
i then carried on to Savanakhet as I needed to apply for a Thai visa, but the accomadation is pretty bad. 1.5 hours north to Thakek there is a great hotel for 25$.
You would need to push it to get to Thatek, before nightfall.
I don't know the route to the west that you take but if you look to make some excursions, the caves around Thatek are nice to visit.
Thatek > Phonsavan .. I took moto-Rex's route, it's very good advice. The 13 may well be a boring road but it will get you to where you want to get quickly, the scenery is nothing to talk about.
When you turn off from the 13 things get better, follow the road to Vientnam to pak ha then turn left, the new road is very quiet, you could make phonsavan in the day, but I suggest an easy day and stopping in Thatom. There are several hydro schemes in the area, and the place has some good restaurants and clean but basic guesthouses. I made the journey in one day, but didn't appreciate the climb to the plateaux at 1100m, the last part was pretty scary in the dark, arriving in the town cold and wet.
The route over the top of the national park is a good hour of twisties and a few recent landslides but the Tarmac good, I saw very few vehicles, say less than 10 after huahoi.
Apart from the jars, there didn't appear to much of interest to keep me in Phonsavan another day.
muankham looked interesting and stopping in the small towns with my versys on the new route caused some interest although people wernt that friendly.
For the return I tried a different route from Thasi (?) to paxsan .. On a heavy bike it wasn't possible, so I took an early day stayed in Thatom followed by a another easy day to thakek.
Tonight I will stay in pakse, to stock up on western food before crossing first thing.
I found the 13 to be a decent road although lots of humps and bridges but nothing really bad, I didn't push over 100kmh the locals seem to just weave about the road without any care and there are plenty of cows/goats/pigs/school kids on pushbikes to avoid.
hope this helps.