The H700/710 would be just fine. It's running at 6g
Just remember, if you have a 12g drives, then change the card out. to support the 12g. It would just set you back about 1K for that card and some real dough for the Enterprise SSD that runs at 12g.
PS: If you run at that speed, go NFS don't get stuck with iSCSi, that's way too much work. New hardware run new tech. don't run old tech with new hardware.
And remember to drop in a dual 10/40gb fc.
Your Answers:
1. Flawless, even with an R510, H700
2. No, the H700 + is already overkill for what you want.
3. No. stick with Dell parts for Dell servers.
4.And beyond, it all depend on your rig. If you want Full Enterprise SSD capacity, then go with something like this.
PER720/30XD
H710/H820,
64GB
Dual CPU Hexa 2.6 up. Really not important. the work is in the RAM.
By the end, you will have 24 SSD drives outspeed the Synology.