I've done some research and believe I know the correct answer to both of these questions, but would like confirmation before I spend the money:

1. On my 2013 Giant Defy 3, the left Tiagra STI brifter (ST-4600) was cosmetically damaged during a crash. It's operating just fine, but I've come into a minor windfall and want to upgrade to 105 brifters while I have the money. I'll not upgrade any other components until they fail. My set up is 2x10, so I believe I need either ST-5600 or ST-5700, as both seem to be 2x10. Is the ST5700 simply a newer model? Is there anything else I should be on the watch for?

2. On my 2013 GT Transeo 3.0 hybrid bike, I'd like to change the tires from the current MTB tread 700C x 40 tires to 700C x 32 cyclocross tires. This is due to the type of riding I use it for, exclusively packed trails with some loose gravel on medium grades. I do not use it for rock-hopping, mud, or any anything else that I would consider true MTB riding. My aim is to reduce rolling resistance on the packed trails. My wheels are 622 x 19 and because I'm going to a narrower width frame clearance shouldn't be an issue. Is my thought process correct?

Thank you for all opinions and facts!