Probably stupid idea but at least I'm running...but advice needed

Hi all. First post and all that, looking or some advice as a new runner (previously lapsed runner due to being stupid and pushing too far too soon!) So I'm 31, 5"9 60kg, so hardly overweight, medically all is fine and I eat well (loads actually) but wanted to get in shape to feel better. I've started running and with colleagues at work have decided to do the robin hood half marathon in September (Nottingham) Now I'm going from almost zero "exercise" but am quite active otherwise. I'm 3 weeks in and happily running 3 miles comfortably, just got to keep remembering to slow my pace though! I have a plan from asics site to get me through the half marathon and so far so good. What I need advice on is what else i should be doing - should I do some cycling, swimming, cardio etc ? Also, shoes... I went to sweatshop and did the motion analysis and walked out in some asics 1170 stability shoes which at first have been great, but as my foot has got stronger they see to be making me overpronate more - in fact today the most comfortable half mile was when I took them off and ran barefoot through the park! I rarely wear shoes at home, only if out or at work when I have to, so my feet are probably not as weak as I thought, and like the idea of "barefoot running". What I was wondering is if it's worth going back to the shop now my foot is used to running and redoing the gait analysis? Maybe a neutral pair is better or the barefoot ones? Probably not quite looking at vibrams but I do like the idea of those. Also would a switch to barefoot mean an end to the half marathon campaign? I assume it'll knock me back a bit so perhaps combine with a better pair of shoes? Sorry lots of questions... I am loving running again though, happy my knees and legs are holding up as well so am a bit obsessed ha ha