I can only comment on part of your tour, maybe someone else can help. I did some of your route last week and last year.
Where will you stop on the first night ? Sisaket ? ( Sorry for the questions, i can't zoom into the map to find the detail )
Do you enjoy the Korat road ? I always run underneath on the 304>Ramkamhaeng>Chachoensao>Sakaeo. The road was awesome fresh tarmac, no traffic and no towns to slow you down, its just straight fast riding, good fun.
Then there are a couple of routes from there, heading North to the 24 .. One of the roads 3462 is under roadworks but there is another route, I have logged on my handheld thats OK. (If you are interested, i will dig it out).
From Buriram > Sisaket > Ubon the road is being rebuilt, single lane. It was a bit tiring for me after a day of riding, but I pushed ahead to Ubon and stayed at Sri Issan hotel, I thought it was nice, the food in Ubon is really good, there is a good vibe about the place. This puts you on better roads, fresh tarmac leading from Ubon centre to Chong Mek. I just find the whole Khao Yai / Korat route so tiring, all those busses sitting in the right hand land, the chewed up tarmac, etc
I had a breeze getting through Chong Mek this year, I printed all my documents before arrival - Maybe I will post a guide here in time.
From there Pakse. No problem, its a big town, nothing going on. You will be there by lunch, you maybe happier heading out to Tad Lo and staying the night at a waterfall resort.
Then the "13" the most boring road ever, you feel like you are riding a camel after a few hours, i hate the surface and you'll be sick of the biggest Laos pickups flashing their lights and bullying you off the road. I don't see any way of avoiding this part of the journey, there is nothing of interest for me at the side of the road. You could stop for lunch in Savannakhet, you can get a good sandwich there.
But, then at the end of the day you will drop into Na Hin ? for the night ? I'm not so hardcore, you might want to check this place
http://recom273.asia/inthira-thakhek/ in Thakhek and push the boat out a little. Also as David says, time Vs distance is greater in Laos. Everyone I met who talks about the 13 is the cows, the pigs, the kids and the buffaloes. You won't want to hit any of them wandering / riding push bikes on the road.
The next day - but there are some interesting bits,
The Nakai Plateau - Limestone Forest loop - southern Laos This is an excellent post -
Update on the road that goes south from Phonsavan to HWY 8 at Lak Ha.. I did it in a day, its a hard slog to Phonsavan, the later stages to the plateaux are hard work, trucks on the road. You might find the later stages a bit tough on sports bikes, theres also plenty of photo ops on this road, you may want to factor that in to your itinerary. So it might be an idea to factor in an extra overnight stop on this section.
I found this place
1D Road from Pak Ha to Phonsavan outside Thathom.
Then the next day, make the ride to Phonsavan. If you leave in the early morning, you will have time to see the jars, and still have some time to relax.
I hope someone can jump in and take over, I haven't done any more of your route.
Hope you enjoy your trip.