FYI, if you don't want to drive to/from the convention, it's possible to get there with public transportation. The commuter rail Lowell line can get you from Woburn to North Station, and then you can take the subway to the convention with a couple transfers.
But an even easier path may be to take the 354 Woburn Express Bus,
which has a bunch of local Woburn stops before hightailing it to downtown Boston near Government Center. From there it's a healthy but doable walk to the convention center, or you can switch to the subway.
As for going alone, all I can say is that I've had a blast at the PAX Easts I've been to, and my experiences have been mostly-solo with sporadic Teggy/Kelric encounters. I'm sure you would have had even more fun if your friend could have made it, but the crowds at these things are so friendly and all-inclusive that you don't really feel alone when you go solo. Pretty much any time I was sitting in a long line by myself I inevitably ended up joining some nearby people in a game of zombie dice or whatever other line-waiting game of choice was going on.
If only I still lived in the area I'd take you up on that 3-day pass and join you in an instant. PAX East is just a ton of fun.