For starters, you might want to start to learn Spanish. Very few PRs actually speak fluent English and the rest might not speak it at all.
Bug? Well, let me separate this in two categories. If you live in a metro area or close to the beach, you're gonna have your share of mosquitoes and cockroackes (the big flying brown ones). Most spiders you will see are the little ones, those who tend to live inside the house. Be prepared to live with at least one lizard inside the house, those things are just impossible to eradicate. They eat the mosquitoes and roaches though.
No snakes whatsoever. If you have lawn, you'll probably have problems with ants as well.
Now, if you don't live in the metro area, you'll probably be living close to the mountains or so, so you might have a bad experience with mosquitoes, roaches, and ants. You'll live with 2-3 lizards. You might see snakes, but PR snakes are non-poisonous and won't hurt you. There is some kind of hairy spider native to PR, as far as I know they are harmless.
You interracial marriage will not be a problem at all here in PR. We see whites marrying blacks all the time. PRs tend to be very mixed race-wise.
People at Metro Area tend to be more angrier because how hectic live if in the Metro Area. People tend to relax farther from Metro Area.
I don't recall a place with race segregation or anything close to that. People in the suburbs and gated communities tend to mind their business, although you will probably have 1 or 2 nosy neighbors.
PR might be cheaper than Hawaii, don't have the facts to back that up though. Word of advice, those "big and cheap" houses are probably far from the Metro Area. Houses in Metro Area are usually not very cheap. Of course, I don't know Hawaii real state market, so they might be cheap when compared to Hawaii. Maybe you could give us an example of one of those houses?
We got a sales tax of about 7%. Only gas is not taxable I think. Other members might say differently.