For G3100, you cannot connect a wireless repeater/extender to it unless the extender is E3200 or WCB6200Q (Actiontec brand).
For third party repeaters and extenders, you need an Ethernet or MoCA backhaul in between.
E3200 is meant to be connected to G3100 via MoCA. This is the intended setup.
Mesh WiFi is, in my opinion, is the least preferred setup. Fiber is better than twisted pairs, twisted pairs are better than coaxial cable, coaxial cable, well, is better than no wire at all (i.e. WiFi). MoCA 2.5 supports 2.5Gbps throughput.
G1100 can be connected to G3100 on MoCA too. You can use G1100 as an extender and disable the functions that would make it a router.