Hi Moorlandwalker.
Welcome to the forum. Over the last 3 years I have been visiting the National Parks here in Thailand for hiking & camping and during that time I have found very little information more than what is available on the websites (which is minimal). Hiking is not very popular in Thailand so the demand for information and maps is low. (even though there are many beautiful National Parks)
The best thing to do is drive to the national park HQ and ask for information when you get there. Sometimes they have very very basic maps, but usually they have trails that are signposted.
The more popular National Parks (such as Phu Kradung and Phu Ruea) have everything you need including bungalows, camping equipment, restaurants etc.
If you go to one of the parks you mentioned (not popular per se, but just as beautiful and interesting, they will have no amenities beyond a park HQ and a car park (and maybe a toilet). If you go there, basically take what you need. If you are going for just a day, then take whatever you need for a day hike (including proper hiking boots and food etc.)
If you want to go camping then you pretty much have to take everything with you also. You can camp anywhere you want in these National Parks (it's not like back home where there are rules about camping). I have been camping quite a few times and the only rule they have is NO GUNS!! So you have to take with you all the gear you need.
I'm not sure about vaccinations. I haven't had any for 10 years. Just make sure you cover up well - especially at night. But it's not too bad when you are camping - you make a fire, which keeps most things away, and your tent will keep you protected at night.
And yes, there are plenty more trails and National Parks around here. In a few weeks I'm going up to NaYung-NamSom National Park In the NW of Udon.
http://www.dnp.go.th/parkreserve/asp/st ... d=239&lg=2 I can't find much information on it except there is a large waterfall. The website says there is... "wild boar, common muntjac, macaque, langur,squirrel, clouded monitor, snakes and birds." I'm not sure if I'll see any, but should be fun. I've not decided whether to go for the day or go camping yet.
If you need any more information just ask. I will post some photos of my next trip to give you an idea of what it's like.
Maybe we could meet up and go for a trip - 10-16 km sounds like my kind of hike.
All the best
Nick