This for a 4x2x2 enclosure
Arcadia 584504 Pro T5 UVB Kit 24W Desert with D3+ 12% Reptile Tube, Approx. 57.5 x 6 x 4.5 cm https://a.co/d/ibD188a
This for 6' or 8' enclosure
Arcadia 584505 Pro T5 UVB Kit 39W Desert with D3+ 12% Reptile Tube, Approx. 87.4 x 6 x 4.5 cm https://a.co/d/5EtvxpC
And...
That doesn't provide much UVB most of us use the ZooMed 10% or Arcadia 12% T5 bulb they provide UVB long in the sense that the strength fades over time.
The bark? If you spot clean and don't have standing water or gnats you should be able to go for roughly 6 months or till it stinks from the tort peeing in there. You can clean,rinse,dry and reuse the bark too.
I would not use the under tank heater. The tortoise get heat from above not below. If they need to regulate their temperature your taking away the ability for them to burrow down to cool off.
I get the cheap throw away aluminum pans from the store and bake it for 30min to an hr at 250°-275° what i did when I replaced the bark was baked the lower layer last and when it was done sprayed some water in pan and mixed it up making sure it wasn't too wet then put it right in enclosure then...
I would get rid of the soil all together and just use the bark. The soil is going to have mold issues and you won't know it's happening if you have it covered with bark. Also make sure you don't have standing water, if you switch to all bark the lower layer just needs to be damp. I do it before...
They can eat shrimp and chicken too boiled plain. Or super worms. A lot of people feed it once a week or every other week. Also Mazuri pellets, mealworms, crickets if you can stand the noise they make while alive. Just to name a few. You can give them the shell with the hard boiled egg too.