1. When you witch from one size cog to another you need to adjust your chain tension by pulling the wheel back in the trackends. Yu want it tight enough to not fall off the cog but loose enough to haveplay. You'll get the hang of it.
2. Thats all personal but a 44-16 is 72ish gear inches so I'd think you'll be okay.
3. Yes. If you are riding fixed you need clips and straps.
4 If you are riding on the freewheel side then it is unnecesary but not a big deal. If you are riding the fixed side only then take the rear brake off. You already have a rear brake with your legs.