First off welcome to NR! This site is a wealth of information...just use teh search function and almost any question you have will have already been discussed/answered previously.
That being said, I'll tell you what has worked for me in regards to your questions and budget limitations.
You will be fine with 1 powerhead. Lighting...I'd get a Par bulb and a desk lamp that you can adjust the height on.
AC20 as a fuge? Nope...you'll want to be able to add filter floss, Purigen etc: instead. Plus you'd need to buy another light just for the fuge.
Just add some macros to the display instead.
Your coral selections are fine...but your livestock choices I'd reevaluate.
Tanaka wrasse (my absolute favorite fish I've kept...Pink Streak Wrasse too)...they require a ton of rock with holes and cracks to swim in and out of to feel safe. if there isn't a ton of rockwork they will just hide...and you don't want that? Plus wrasse are constantlyhunting...so goodbye to any pods, worms, snails, shrimp (that will fit in their mouth)...basically any clean up crew you have will eventually be
harassed. With no clean up crew, your maintenance schedule must be aggressive and diligent or else the inevitable algae issues will pop up.
Clowns (or poop machines) will also require diligent maintenance.
If you search you'll see that in the long term most of the successful smaller nanos usually start with inverts and maybe a goby or two and then as the tank matures move on to bigger fish.
I'm not saying that what you're proposing can't be done...it's just going to be a lot harder for you. And everyone is trying to set you up for success!
Hope this helps