Hello and welcome to the forums!
I ain't very knowledgeable in the building of PC's, but may want to post your budget or the estimated amount you wish to spend for the upgrade to help the others in their recommendations.
Regarding the 1 stick of ram... if I read correctly, you may be restricting yourself somehow. Don't know how exactly but I believe you receive a benefit of some sort having 2 sticks instead of one.
<-- I have been learning from reading the vast PC building posts and by others recommendations.