new gmail account and purchased apps.

So my current google account is linked to my yahoo email since that is the e mail I used for youtube and google+. I made a gmail account with a more professional name and have heard about linking other emails with gmail. I tried and was a bit confused. When I tried all I could find was a way to just important mail to my gmail from yahoo for 30 days which isn't what I want. What I want is to be able to link my yahoo to my gmail so that when ever someone sends a e mail to my yahoo account it also goes to my gmail as well. Is that possible to do? Also of that is possible and I link my yahoo with my gmail could I log into my android phone with my gmail and still have the apps I have purchased or would I have to keep logging in under my yahoo?

By forwarding does last forever or only a certain amount of time? As for logging into multiple ggole accounts on your phone I am aware of that as I had my yahoo e mail and a different gmail logged in at the same time. I have noticed though that when I log in to those two different google accounts accounts on the pc the yahoo account is missing some apps. It isnt a problem now since those apps are on my phone and they were free. If logging into your phone with 2 google accounts does the first one you log into count as the account your apps and such go to?