1) Yes you can upgrade, though I would recommend just getting the R5-2600 to start since it's not much more than the R5-1600.
2) The R7-2700X won't necessarily be much of an upgrade unless you use applications that can utilize the extra two cores.
3) Memory should first be Dual Channel (two sticks, see motherboard manual for proper config) of either 2x4GB or 2x8GB depending on budget and at least 3000MHz.
For example:
2x4GB 3200MHz CL16
4) I recommend x4 DIMM slots (not 2) so you can add memory later.
5) which motherboard boils down to the budget. Lots of choices there. The quality/reliability is going to factor in. Will be differences in audio quality and other features too.
6) I'll attempt to post an example of parts but you'll need to help give a budget etc.
7) finally, X470 allows for STOREMI (hybrid SSD + HDD option) but your budget might not allow that.