fios and eero: help  

have had fios (symmetrical 1 g) for years and have had no trouble at all.
flummoxed installing eero and fios.

mixed system: iPhone, mac book pros, windows 10 (mostly without WiFi thus wired) with two wired printers (and one wireless printer).

need to keep two networks:wired and wireless legacy stuff on fios network, newer devices, mostly iphones, pads on eero WiFi.

first turned off WiFi on fios: LOST my wired setup printers and wired legacy devices.

then turned on WiFi on fios and left eero WiFi on.

now I have both WiFi networks. seems to work fine.
is this wrong headed and a beachhead for trouble???

any help would be great.
thank you.