Just start on what you have now, it will be able to run BOINC if its 5 years old and you dont need to worry about the cost of buying something new. Seriously, just do it today, download BOINC from here and then once its installed go to Add Project and just choose one, World Community Grid is popular.

Once you have BOINC running with a few projects you like, and its all going smoothly, you can then add Gridcoin and perhaps buy some new equipment. Then you can worry about optimization etc., but the sooner you start, the sooner you finish.

The best way to learn is to try:
I hear; I forget
I see; I remember
I do; I understand