If you are trying to do a two day 180 mile event in five months, you REALLY need to ride more than once or twice a week. At the very least, get a trainer and ride at home (I hate riding on trainers, but do it if I can't get out and really want to/need to ride).

You can also take a spin class and put the kids in the gym's daycare thingy. Or pull them in a trailer.

Regarding clips, as someone said, they help you make the most of "all" of your muscles if you are pedaling properly. If you don't have clips, you'll burn out your upper thighs from pushing down only. I got used to mine pretty quickly. Do your research and find clips that people say are easy to get used to. I have Speedplay and love them. They have "float", so I can move my heels a little left and right and not be completely "stiff". I can't even imagine doing 180 miles without clips.

As for shifting, one thing to keep in mind is that the harder the gear you are in, which you might think you like, the harder it is on your muscles. If you watch the pros on TV doing 100+ miles daily, you'll see they "spin" there pedals relatively quickly. It's the inexperienced or unkowledgeable riders who are "grinding" in a slow gear. However, spin too fast and you'll be working your cardio more and breathing harder, so finding that fine line for you is what you need to do. The more you can "practice" using a faster cadence on some training rides, the more it will become natural and you'll realize you can rider longer without wearing yourself out as easily. So while some people "like" to grind in a harder gear and might feel they get more power and can ride faster, it will only last so long, especially on a 180 mile ride.

The most efficient riders shift often, even on little "whoop dee doos", like going under a freeway overpass on a bike trail, or even more mild than that. The goal is to stay in your cadence, whatever gear that means. If you are riding along a flat path at 15 and spinning at a comfortable cadence, and you see a mini hill coming up . . . it might only be 20 feet, the most efficient way to get up those 20 feet is to shift to an easier gear or two just as you begin the climb, then shift right back when you level out again. As a beginner, don't get yourself all worried about that right now, but it's something to keep in mind and work toward. I mainly mention it because doing 180 miles is no small deal and the more you know the little tricks to extend your energy and muscle strength, the better.

I've done a lot of centuries and some with a heck of a lot of climbing, but the furthest I've ever done is 150 in a two day period (75 each day). I was stressing about this even after having done several centuries. I just couldn't imagine getting on that bike a second day after after riding 75 miles. However, I was pleasantly surprised. It wasn't that difficult at all. I say that with the reminder that I had a whole lot of "base miles" in me and had been riding for at least two years, maybe three at the time.

Base miles is what you need, why you need to ride more than once or twice a week. The more miles you ride, even the shorter rides which add up, the more your body gets used to riding and the easier the longer rides are.

As for speed, what others have said about 15-ish being "average" is probably the best guess anyone can give. It really depends on the group. Typically, depending on how many riders there are and their levels, group rides will split up between different paced riders, but they may regroup at various places and take breaks together.

Don't underestimate the power of drafting. This is something best to be taught by experienced riders, but if you can practice this technique before your big event, you can use that skill to save your energy and muscle strength. If your husband or another rider (or several riders) are "pulling" you (not actual pulling, of course), they are breaking the wind for you (even if it doesn't feel like there is any), and it makes it easier for you to go faster and farther. Lance Armstrong didn't win all those Tour de France races by riding alone. He had all his team mates pulling him throughout most of the rides and he used all his energy to take of at the end of the stages and win.

Hope all this helps. Good luck! RIDE AS MUCH AS YOU CAN!!!