At 19 years old, I think money is probably the limiting factot (I know it was when I was 19 and still is and I am 36).
Keep the 377 and put a nice healthy solid cam and a 3000 stall in it. This will get you where you want to be. Get a single plane intake and call it good. If you decide to build the larger engine in the future a cam will be a small expense in the grand scheme of things anyway. So buy a cam that will work in the 377 and if you build the other engine later just buy a new cam at that time. You can't have it both ways.