Betta Fish: White Elephant Betta, what can I improve?

Surprise surprise, for my company white elephant gift party, someone followed the trend on Tiktok and got a live betta fish. I was so genuinely excited I swapped for him immediately so I could take him home.

At the very least, the gifter was kind enough to supply a tank, some decor, food, pretreated betta water, etc.

I set up the tank and immediately introduced Alejandro (my new little red boy) to the tank. It's been three days now; I'm obsessed. I bought live plants, blood worms, and almond leaves to help with the nitrate cycle and for stress. I want to give him the best quality of life I can, and wanted to ask advice!

After scrolling through this subreddit, some immediate improvements I want to make:

Upgrade to a 5 gallon tank: Question is, can a 3 gallon be okay short term, as long as I keep it clean and cycled?
Duckweed! I'd love to do the duckweed cover on the tank with the feeding ring…would that provide him enough air, though?
Tank background wrap: I've noticed him glass surfing quite a bit…and anytime I come into the room or look at him in the tank, he flares at me…would having a dark background or busy one help with that?

Speaking of him flaring at me(is that normal?), I've also noticed a TON of bubbles on the surface of the water…they're not in a bubble nest formation, is that a good or bad sign that they're just kinda scattered everywhere?

Any other tips and suggestions would be appreciated!