Whether you speak fluent Spanish or not; Pick up a copy of Lonely Planet's Costa Rica Spanish Phrasebook with two-way dictionary. It will be the best investment you ever make. I cannot emphasize this enough.
I haven't been to Cartago, but it's going to rain, probably every day. Its no biggie... kinda like Florida in that it will be beautiful before and after the rain.
Since I'm not a woman, I can only make educated guesses on how you'll be treated. I did see quite a few foreign women, but didn't spend any time with them. They seemed to be quite comfortable and having a great time. If you are staying at a decent hotel, they will register any and all "guests" you have, so there is little to worry about there. Use common sense and don't travel alone. North Americans are treated with additional respect by and large, so shouldn't have any problems.
Don't wear any Gold or expensive Jewelry, and leave your nice watch at home. If your outfit has pockets, don't bring a purse. Take only what you need. There will not be any need to ever carry more than $200 with you, regardless of where you're going. If someone puts their hand out, give them a coin. Don't be shocked if asked for the last few drinks of a soda in public. Giving it will not encourage further begging (at least, that's been my experience). Ticos bargain: If you are quoted a price that seems high, don't be afraid to name your own price. No mas de dos mil Colones ($5).
Tipping restaurant and bar people is unnecessary, but is always greatly appreciated. Use your own judgment.
You are going to be the most popular person, everywhere you go. Don't get freaked out by the stares; Ticos are very open in their admiration.
Most everything is cheap, so have fun. I don't believe they enforce drinking ages, so be careful what you do and DON'T GO OVERBOARD!
If you spend any nights in San Jose; Eat at Ram Luna (incredible) and party at El Pueblo. There is plenty of security at both places, but again, use common sense, too. Ticos live to dance, so if you do too, El Pueblo will be the jewel of your trip.
You can find more of my ramblings on the subject
here.
Since quite a few well-traveled A2Kers have already marked that thread, you might be able to get additional perspectives by typing a question there. Good Luck! And enjoy your time in Paradise!