OP! Welcome to this wonderful world that is ski building man. I to am currently building my own ski press and firstly to answer your question of press vs bag? I'd honestly recommend that you build the press if you have the time, resources and money.
Press Vs Bag:
Cost- The press will cost you waaay more money than a vacuum bagging setup ever will. I've gathered just about all of my materials for my press and have quite a bit of it completed. I've done some hunting to to get some materials on the cheap. With that being said, a rough estimate on dollars spent on my press is about $1400-$1800 CDN. It's not cheap. A turn key vacuum bag setup and mold will cost you at most 800, and I'm sure you could easily acquire the gear to vacuum bag at a much lower cost than that.
Skill- The press takes alot of free time and some decent knowledge of shop tools and equipment if you plan to do most of it by yourself. I probably have 30-40 hours of raw time cutting, welding, and grinding on my press, and I'm probably just over halfway done. A vacuum bag setup doesn't require as much 'shop; skill and it is much quicker to get a working setup.
Quality- Now both methods can produce some very nice skis, but a ski press will apply much more force to the ski and the pressure can be adjusted accordingly in turn producing a stronger ski. A vacuum bag relies on the outside atmospheric pressure to apply a force to a ski. This force is somewhere around 14psi. In regards to your comment on altitude, the closer you get to sea level ( 0ft ) the more force will be applied because there is more atmospheric pressure at sea level. Ideally, all vacuum baggers would be pressing in death valley :D below sea level, and LOTS of heat!
Convenience- This is somewhat subjective. After doing a full layup, it is much easier to slide the sandwiched ski cassette into the press cavity, and turn up the pressure. A vacuum bag requires that you make sure you have a good sealed up bag, and only then can you turn on the vacuum pump. It does take a little longer to get the pressure onto the ski in a vacuum bag as opposed to the press, which can be costly if you epoxy starts to gel and harden before you get the vacuum pump going. Size wize, a ski press is a pretty large shop tool, and it will likely get in the way if you don't have a good place for it. A vacuum bag setup has only a few parts, the mold being the biggest part, and a mold is sizable, but easy to store. If storage is an issue, a vacuum bag setup is the way to go.
In the end, like I said, I'm making a ski press, I have the time and would like to think I have the moeny, and storage isn't a major issue for me. I also like the convenience during the layup process, and a big burly press is just another man toy for me :D
As far as help from people and places go in your journey to build skis, hit me up with anything, and I'll try to help you. NS Members KyleA (who's already posted in here) and hot.pocket (his dad has helped me out alot aswell) have been nothing BUT helpful. Extremely knowledgeable on the subject and have hooked me up with some very useful knowledge and pics etc.... Iggyskier and Ginko are another good set of guys (They're from ON3P)
Links:
My Ski Building thread on NS:
https://www.newschoolers.com/ns/forums/readthread/thread_id/651776/
Ski Building website:
http://www.skibuilders.com/
Ski Building forum:
http://www.skibuilders.com/phpBB2/
Good source for materials:
http://www.skilab.com/
Good luck with everything man. Read around before you take my word for anything just yet though. I may have screwed a few things up in there, and I'm only really knowledgeable on the basics of the process. Enjoy!