I haven't seen that hotel but its location is halfway between Lisbon and your friend's town Monte Estoril (which is actually simply part of Estoril).
You won't really need a car. There's a a train line running parallel to the waterfront linking Cascais-Estoril and Lisbon. Carcavelos is one of the stops in between. It's a suburb known for its large beach. For fun, dining, etc., I suggest you go to Cascais, Estoril, and of course, Lisbon.
Have you taken a look at our Cascais and Estoril pages?:http://www.golisbon.com/portugal/cities/cascais.htmlhttp://www.golisbon.com/portugal/cities/estoril.html
Enjoy your trip!