I like your idea of the modularity, and I really like the size of the pouches you are considering. I toyed with the modular concept for a while, and at the time considered using U.S. military surplus first aid/compass pouches. I have not pursued that configuration because I didn't want to look like Batman with his utility belt, and also the first aid/compass pouches were too large for some of my modules. These pouches you have selected are another matter, and I think you will be more successful with the idea than I was.
I agree with miniMe about building your kit(s). There is no substitute for advance planning. Daydream (but not while you're driving!), mull things over, doodle and write things down. Check out other people's kits, and don't be afraid to build on them and/or improve on them.
You could probably do a search on PSK to find most of the kits here. Also, there is a dropdown menu at the upper right of most screens, and on it you will find a number of options that will lead you to more good info. At Gear and Equipment, for example, there are discussions about Gear and Equipment (!) and also Doug's evaluations of several other kits. Doug also lists several of his own kits at Doug's Kits. Skills & Technique is good reading, as well. As you read, you will probably get all kinds of ideas of things you may or may not want to include in your own kits.
Let us know how things go and what you come up with! Go for it!