Hmm, the 'My Asics' training plans are not great. I've just got it to prepare one for me and it suggested I do 22 miles at race pace 3 weeks before the race, which is marathon suicide, as far as most people are concerned. Particularly if you're only doing 4 runs a week, which is the most it will accept anyone wants to run. So, my first comment (probably not what you wanted/expected to hear) is change training plans. Try the ones on this forum or Hal Higdon's website.
Gels: I did use them on runs over 15 miles (that's about 24km) when I started running marathons; now I don't take any fluid unless I'm running over 18M (29km) and only bother with energy stuff over 20M (32km). To an extent you want to train your body to use its own fuel reserves. I've never bothered with electrolyte tablets. It's cheaper to just use jelly sweets and make up an energy drink from a bit of fruit juice, a pinch of salt and some water. Use gels on a couple of training runs (preferably ones where you are running at planned marathon pace) just to make sure you get on ok with them.
Good luck.