When i have parked a domain, can I still link a page to it with advertisements? and will the hosting company only allow me to have a certain amount of parked domain names?

If you park it, most parking companies do not allow you to have links on them.

And you can park as many as you want, these are no longer hosted by your hosting company, but by the parking company, so you should not be paying anything for hosting.

Cheers
David