People would much rather have these animals rehomed than risk them being hurt/mistreated (not saying that you will but some people lose interest then fail to care for them).
Once you have that 6-7ft viv that would be a much better size for housing 2 beardies than one 4ft. If you choose not to rehome then make sure you have the back up plan that can take them in at short notice.
Read other threads about breeding. With beardies you will make a loss and there are so many unwanted ones already, adding to the numbers isn't a great idea.
Not sure what reviews you've been reading
again look at threads about it on here. There was a very recent one in the lizard section and a couple of well respected breeders said that they'd only use it for certain species of gecko. At the end of the day, a lot of the manufacturers are in it for the money (hence it's so expensive) not necessarily because they have a passion for the animals. I found calci-sand very messy. Stains the animals and if it gets damp it forms solid clumps and is quite dusty (not good for respiratory systems). Your call but have a look at negative reviews too.
You don't need a thermostat for UVB, you'll need a dimming one for the heat bulb. Watt wise you just need a thermostat with wattage that's more or the same as the watt bulb you're using. I forgot to ask what kind of UVB you using? Is it a coil or tube?
If you're good with timings then just keep with what you're doing. For forgetful people like me we use timers.
What is the reptile shop that you're near?