Iian,
Forget about Dominican men, you'll be good for me. Yes, Finnish girls are the best in the world except for one fault - they think that I'm too old for them now and won't give me the chance to prove otherwise. Oh well, I had my time in Finland - very nice.
Yes, I still remember how to say "kiitos", accurately, I might add. I could also say "kiipis", but I never tried to learn Finnish. Sometimes it was better, it seemed, not to be able to talk with the girls. Of course, at least half of them spoke English anyway.
I hope you know Spanish. The Finns may be the world's best linguists, and you obviously speak Finnish, English, Swedish (of course), and maybe German and Russian, but Spain is far away. Start studying if you don't already know it.
Also, you desperately need a crash course in being "street aware". Those who say that the DR is "safe" are comparing it to New York. Coming from a place where women entering a discotheque throw their purses into a pile in the corner, then go back and get them when they leave (for example), there is no way that you are prepared for the DR. Maybe your travel agent can give you guidelines for surviving in a third world country. Most of it is common sense, but which you haven't had to consider in Finland.
Upon your arrival, you should be very careful about going anywhere alone until you get used to the culture, and become "street smart".
To answer some of your questions:
1. Mao is probably as safe as anywhere in the DR. It is poor and thus probably has a relatively small criminal class. Petty theft, though, is rampant everywhere in the DR.
2. Los Girasoles must be a barrio, but I don't know where it is. Duarte Street goes right through the main residential area, so if you look at a map, you might find it in that area.
3. I don't think you'll need to go to Santiago for nightlife, unless you're trying to meet Gringos or rich Dominicans. The DR has discotheques everywhere, just like Finland - no town or barrio is too small. Agua Azul is a popular place. It actually consists of the best hotel in Mao, with attached swimming pool. Normal admission to the pool is about 50 pesos, I think, except when they have a band, then it might be 200 pesos. The pool has a bar and a large seating, dancing, area.
If you do want to return from Santiago to Mao at night, you might be able to find a relatively late bus (Caribe Tours, for example) that passes through Mao on its way farther west to Santiago Rodrigues.
I don't recommend taking a taxi cross country at night. Since there are no police patrols, even Dominicans don't travel at night except in groups. Santiago to Mao might be marginally ok, though. because its not really open country, but has little towns along the way. It might cost about 500 or 600 pesos. Bus fare should be no more than 50 pesos.
Prepare yourself, but relax - you'll enjoy it.