I've only gotten to play with cable stuff once- everything else is ADSL/VDSL. Most of the pure modems for that have a nonpermanent LAN address, some have a DHCP server as well. I had to modify mine to a static address.
If you can manage your modem at all, see if you can turn on a DHCP server on the modem. It's janky as all hell, but it makes plug-and-play possible.
If not, it may be possible to set static IPs on the modem and the router.
I agree with @Piemanfood, and would like to add- RAM is basically plug and play at this point as most of the bad RAM manufacturers are gone, and that case is a bit, uh, expensive for a budget, yeh?