I would go for a 300w thermostat, yea a 100w can handle US29g (I think) but it'll be stretching it abit.
My 22gUK has a 300w thermostat and it runs perfectly as it's not having to work mega hard as it's more than the tank needs.
Same with your filter, I'm not familiar with a 20/40 but I'd recommend whatever you go for you get a more powerful filter than you need (especially with canister filters - fluval 304 or equivalent for your tank size I'd suggest).
Plants you could add. Thermometer (glass internal one), bucket for water changes, strong jug for water changes, tap safe declorinator, net, algae magnet cleaner, algae scraper, siphon, gravel vac (possibility), bogwood (possibly, if you're planning to get a pl*co
).
There's much more I'm sure, that's off the top of my head.
Oh, and one of the most important things, a chemical test kit (if you don't have a kind LFS to test your tank water for you).
I know you're on a budget but alot of the stuff above is pretty essential (see if you can get some of it thrown in from your LFS since you're spending enough anyway!)
I'm good at spending other peoples money! Even better with my money!!!!
Good luck!
Pete