I had the same question when I first started. Driftwood will temporarily lower the pH of your tank. Some people also mess around with peat in their filter, which softens your water and lowers the pH. Honestly though, particularly if they're tanked-raised angelfish, they should be fine at 7.6. My cardinals have no problem at a pH of 7.4-7.6, and they're generally considered far more sensitive than angelfish. I've also kept angelfish at this value, and they did fine. It's better that the pH be consistent at a higher-than-ideal value than to mess around with pH changing products and have it constantly in flux.

If you're at the top range of your kit though, I'd invest in a "high range pH" test kit to make sure it isn't any higher. 7.6 is okay, but if it's in the 8+ region, I'd start looking at keeping african cichlids (which like high pH) rather than south american species.

If you're really set on changing the pH though, the only real consistent way to do it (in my opinion) is to use RO water and add the minerals in yourself to set it at the ideal range. This gets very expensive, particularly if you don't want to invest in an RO unit, so I honestly wouldn't worry too much about it. If you were keeping discus, it might make more sense.

Also, 10 gallons is far too small for an angelfish as they age. I've read the same thing as you, but the "1 per 10 gallons" rule only works with larger tanks when people want to keep more than one angelfish (even then it's kind of questionable). The absolute minimum you should be keeping a fully grown angelfish in is a 29 gallon, and even then I'd only be comfortable keeping one of them. 20 gallon won't be tall enough IMO. If you're planning on upgrading within the next year, then you can purchase one now, but otherwise, I'd stick with something size appropriate.

Also, while bamboo can be submerged for a while, they aren't actually aquatic plants, and will eventually rot in your tank. It's unfortunate that Petsmart/Petco continues to sell them.

It shouldn't be too many plants. If you're worried about it, you can invest in some liquid fertilizer solutions that they sell. Some of the smaller vallisneria species might be an ideal choice for you, especially with your hard water.

I would keep up with the water changes. They're especially important with smaller tanks like you have.