Advice on selling sofware, licensing etc.

Apologies if this isn't the correct forum, and I appreciate the question(s) are more of a legal nature than they are programming, but am just asking on the off-chance that any developers here have personal experience or knowledge on this..

I'm a newcomer to java/development, and am learning the ropes. I've got an idea for an application, and think there's a gap in the market for it.

The application isn't huge, and would be mostly j2se api based, but there is a case for using a couple of third party libraries too.

One of the libs is open source, and another is commercial, ie have to buy a license.

In both cases, where do I stand with regard to incorporating these libs in an application which I then sell on myself for profit?

Before anyone gets heated, I'm not some evil capitalist type trying to exploit open-source and make a quick profit on somebody elses hard work, it's just that the software they've put together is extremely useful, and provides a necessary function in this application. I'd be more than happy to give the developer(s) a royalty, for their work.

Or is it just not-allowed, to re-use open source licensed sofware in commercial apps?

The other, commercial library, I'll put the question to them but generally is it also forbidden to incorporate these in an app you're going to be selling on yourself? Or once you've bought a license, are you okay to do that?

Any personal advice, pointers, book recommendations, etc gratefully received.

thanks in advance.

The open source software will have a license that hopefully explains what they allow.
There are several different ones.
It may be as simple as including the lib, along with the license and a note saying you are using it.

The commercial one depends on the company, so you'll have to ask them what alicense costs for distributing with your stuff.