Hi,
I would recommend the digital acurite weatherstation with probe - you should be able to find it for about $12- $15 and it will be a lot more reliable than the little dial gages. Sadly we have found those to be extremely inaccurate on occasion - the other peoblem with them is people stick them half way up the cage wall rather than in the hides where the snake actually spends it's time so the real temps from the snakes point of view can be way off.
I would definately start the no holding period now and, while you could offer in three days in his tank if you like, don't be surprised if he doesn't take it.
If you plan on feeding live you should plan ahead for refusals and have a little critter keeper, water bottle and food on hand for the weaned rodents.
If you feed frozen remember you can only re-freeze a maximum of one time as after that they tend to split and stink to high heaven.
Make sure the little guy has nice tight, snug fitting dark hides to make him feel secure as well.
He probably is drinking but the best way to try and rehydrate them would be soaking them as described previously and that would also stress him out a little so I'm not sure it's all that good an idea just now.
dr del