Choice of 5V connector for power
Micro-usb tends to be SMT only. And since you think 2.1mm sockets are too bulky, usb B (and non-standard A) are out of the question. So go with the next standard. Mini-USB. Same pcb area usage as micro-usb, and still very popular and in current use as it's only just being phased out of devices.

This molex part 0548190519 for example, is a Through Hole Mini-USB B connector. They also have a mini-usb AB, otherwise known as usb-otg connector. The pins are packed together, but nothing that anyone who's ever tried soic or sot devices couldn't handle. It's a cinch.

Alternatively, you could solder on the smd mini or micro usb connector, and leave the rest to the people who buy the kit.