Hi Brenda, your questions have been answered but I'll give you mine.
1, I give my table a rub with 400 wet and dry sandpaper then use Chestnuts Woodwax 22 and buff up. Don't use anything with Silicone in it, it'll play havoc with finishes
2, I always pour my Danish Oil back into the tin, leaving it in the container will do that. Having said that by the time I've nearly used up a 500ml tin it also is starting to thicken, the thinners have been evaporating every time I open the tin.
3, Once you've set the tension with the back knob leave it alone and just use the lever at the front, that's what it's for and why it's called a quick tensioner.