Nice work doing all the research! Much better than buying a board because some guy on this forum raves about his own board for no other reason than it's HIS. I'm no expert, but just bought a new board myself so I know where you are comming from. I've ridden for a long time, but I was pretty unfamiliar with the recent board tech. I'll try to help by addressing a few things:
GNU and Libtech are both great brands made by the same companay, Mervin. Definately include them in your search. Forum is also very good as well from what I've read.
I wouln't worry much about the base. Sintered is better, but nothing a begginer would notice and my understanding is it needs to be waxed a little more. I got a sintered based and learned to wax myself so I don't have to go to the shop...pretty easy and kinda fun is a sick, obsessive sort of way.
As for size, the range you mentioned is about right, but could go up or down depending on preference and comfort. I'm 6'4'' 200 and ride a 167 freestyle/all mountain board and it works great. I learned on a 165 so that's what I am comfortable with. If I ever get another board for more park stuff, I'll go down to 158ish.
For a lot of the other tech stuff...honestly, I'd say don't worry about it too much. The size and stiffness are probably the mian things you will notice so focus on that. The rest of the stuff you won't notice once you adjust to your new board....which will take time no matter what board you get.