Anyone from Costa Rica? Visited Costa Rica? I need vacation advice please!?

So my 4 guy friends and i are taking a senior trip this summer to costa rica. We have been saving a lot for this trip and need it to be super fun. I know its rain season in june/january and we would have to go during one of those months so which month would be the least wet? Whats parts of costa rica are the best? For fun like ATV, beach, scuba diving, also somewhere with a fun nightlife. Do you recommend staying in one part of costa rica through out the trip or traveling and staying in different cities? Any advice would be helpful! Thanks! And we're thinking we stay for a week.