It is a beautiful place to visit but the Dominican Republic is nothing like you might be used to in many European holiday destinations. Most of the hotels are pretty isolated with no nearby shopping streets to wander up and down. There are some shopping malls outside of the hotels in the Bavaro area and Sosua in the north and Bocca Chica in the South are small towns with hotels on their doorsteps.
It is also pretty undeveloped when compared to much of Europe. Outside of the hotels you will see a very different way of life, I have to admit I was pretty shocked on my first visit but once you get to the hotels you wouldnt know what's going on outside. Most are huge complexes with acres of tropical gardens with the accommodation set out in buildings within. The beaches in the South and East are more white sand with the North, being on the Atlantic, more yellow. Some hotels are so large they offer little trains to ferry the guests around their premises.
The weather is hot all year round but there will also be tropical rain showers, which are very heavy but usually very short and not at all a bother because they are also very warm. Hurricane seasons runs from the beginning of June to the end of November. Historically most tropical storm/hurricane activity in the Dominican Republic's part of the Caribbean has taken place in the months of August and September. We had three days of a tropical storm last Sept/Oct and spent most of the time in the pool, where you're going to be wet anyway.
I've always felt very safe there I just take the basic precautions of not flashing too much wealth and wear my bag either across my body or round my waist to prevent the motor bike snatches that seem to be occurring in many places all over the world.
You won't need a lot of money if you don't intend doing any excursions. 10 US$ each for your tourist card to get in and 20 US$ departure tax each but please check because I have heard rumors that it might be increasing slightly this year. Other than that I usually take plenty of 1 dollar bills for tipping, which you don't have to do but please remember the staff work very long hours for very little pay and it makes a difference to their standard of living.
Travel insurance is very important, medical treatment in the Caribbean is very expensive. You should also take advice from your doctor in regard to any inoculations and malaria prevention that may be required.
I could go on forever but I think I've answered your basic questions, please don't hesitate to ask further, I love to talk about the DR.