Just my opinion:

1) I would go for matte display instead of the touchscreen. I had had a touchscreen laptop from HP for a few years, but hardly used the touchscreen itself. Now I changed for matte display and it seems like a better choice.

2) I would definitely go for an SSD - at least for the system partition, it's a small miracle.

3) I'd say 1366x768 is more than enough. The only time I've felt I'd use more was when using the SailfishOS emulator (540x960), but who uses the emulator for development anyways

4) My favorite size is at around 12" for the mobility, but it depends on the use case, so it's up to you.

By the way, if you're a Linux user, try considering ThinkPad. I got myself one (X220) and pretty much everything works out of the box, so it feels like heaven compared to my previous computers.