1

From Praia Lopes you need to walk the short hike over to the nearest 'town'. From here, there will be a few guys selling tickets back to Abraao. From memory it was only about 30 Reais.

Though I found the walk back to Abraao a bit easier.

Try your hostel. There are also plenty of them about. I cannot remember the cost of mine. But it all depends on what tour you take (most companies do very similar trips).

2

The hike to Lopes Mendes is absolutely beautiful. It took us almost an hour and a half to get there. Bring water and a couple of sandwiches (there's only a guy selling sodas and beers in Lopes, and as you might think, they're expensive).
Before arriving to the final "leg" of the hike, you'll see a couple of people asking the tourists if they want a boat back to Abraao. The ticket costs us 15 reales per person and the boats leave at 2-3 pm. Don't worry, you don'tt need to book it in advance.
Snorkelling tours: there are many tours operators, so I suggest that you take a look at some of them. Sometimes, they make group discounts.
Enjoy!