finding separate modems and routers in 2019

[tripletopper]

A few questions about trying to get my Dreamcast online in 2019. And if I do, I'll gladly pay for the service:

1) I heard a problem is you have to have a separate router and modem, and a gateway won't cut it. But finding a separate modem in 2019 is tough. BUT...

I heard you can make an outer (outer being closest to the street in terms of conneciotn pathways) gateway a modem, by turning off the routing features on it, like more than one output, and WiFi. And then you can use another inner router. I heard you can use a wired, wireless, or a combo and it would be fine, as long as it doesn't have an input for internet source connections, like a DSL Phone port or a Cable Coaxial Cable.

2) are there certain brands of modems and or routers, and or gateways converted to modems to use or not use. The reason why i ask is because the gateway is programmed by the DSL company, and they say only use their gateway. They have no pure modems to offer.

3) By the time Labor Day of this year comes, we'l have fiber optic internet. If I can't find a pure modem from my DSL company that works, should I just wait for fiber optics to come in and see if THEY have a pure Modem?