I'm a 40 Year old, which probably is very old compared to some of you here, who play GW.

I started playing around 9 months and I'm a very casual player and looking for some general advice. Some questions that Wiki is not really going to answer for me.
I play about 4-5 Hours a week. I can go a week or two without playing hence my slow progress. I've got Prophecies and Eye of the North installed. My Character is a Mo/Me and I just made it to Level 20, I'm sure others can do that in a weekend, but I'm old and play very casual.
So here are some questions

I've been looking at some builds and wanted to utilise them and improve so I can join teams or others and be able to effectively help them, or be able to go farming on my own without having to rely on 6-8 Henchmen. But it seems I wont be able to build most of the popular builds unless I buy the other campaigns? If thats the case should I bother with GW2 around the corner?
Am I wasting my time with Mo/Me? Should I go with something else?
When I first started playing, this guy who was like lvl 15-18 helped me and a few other guys to farm/level and he was amazing. Being a total noob, I didnt think to see what character he was playing. But he had an army with him. He would res all sorts of minions out of the ground and bring with him.
I Hope I didnt break any forum rules with this post, I did the Q&A before posting this.
OH one other thing, I did join a Guild about 4 months ago and then the leader quit and so did everyone else and all of a sudden I'm the guild leader. So should I keep the Guild? Is there any benefits of keeping it? other than I can go into the Guild Hall?