Well I haven't needed such a thing (open ticket) recently, so check with the agent/airline for the latest info on what you can and can't do with it.
Normally such tickets are valid for one year though, and as long as you come back within the year...no probs. You just get a travel agent there to book your flight out when you're ready, giving at least a weeks notice. They'll charge a few hundred pesos for the service. Also will extend your visa for you if you want.
I never book hotels in advance...never had a problem. You can then easily change if not to your liking. For a first trip (is it your first trip ?) Probably best to book a room online for a day or two though while you find your feet.
Oh, of course you MUST have a return or onward ticket when entering the Phils.
