Hi Inglewood fan,
My background = HT enthusiast (and I do this for a living
).
A couple points:
Epson are nice projectors - good choice.
Screen size is good, three feet for speakers is a little tight but should be fine.
The match up (timbre matching) is not really that important for surrounds (fronts - it can be noticeable).
I have done two subs in a HT room and it helps smooth out the bass. They were the exact same models so I am less sure how well it will work for you but no harm in trying.
Placement is important (there are a lot of moving parts in figuring this out). General rule is to have one sub 1/4 point on front (screen) wall so in your case 4'. The second on the halfway point of the opposite sidewall (ie 16.5'). So left side on front wall with right side wall or vice versa.