You haven’t mentioned what sort of access link or speed you have, that seems very relevant here.
For my 1Gbit/s fiber connection the Edgerouter 6P has been pretty good. It has an SFP port and can route 1 Gbit/s of traffic without issue and my dual-stack setup works well too.
The only significant downside is that its switching is slow, it has no hw support. So I put my NAS on a separate subnet instead so that the traffic to it can be routed instead.
Yeah of course! Once I went on a buying spree of used WNDR3700. They were so cheap and I won a few too many bids at once.
I gave one to a flatmate when we lived together as students and he took it with when he moved out. Put one in the office room of my current flatmate and still have one or two in reserve. I usually take one with me to LAN-parties.
Before that I once used DD-WRT on a WRT54GL. It also wasn’t bad from what I remember.