If you on a tight budget by the best 4 channel amp you can afford, aim for 4x75-100W RMS.
It would be a waste of time buying a 800W nominal speaker if you only have 250-350W RMS to power it, so I would look for a more efficient speaker, perhaps with a nominal power rating half of what you are looking at.
At the end of the day however speaker power rating will not mean much to you at all, I would be more concerned about the sound of the speakers you choose.
The 4 channel amp will allow you to run a sub and your front splits, less cost, wiring and hastle than running multiple amps.