Before you go out and buy your own equipment please for the love of all that is holy don't try and cheap out on stuff like this. DOCISIS3.0 8x4 channel is junk plain and simple. The stuff that Comcast gives people on the low end is basically this https://www.amazon.com/NETGEAR-Cable-Modem-Router-Combo/dp/B078FBC499?ref_=fsclp_pl_dp_1&th=1 but with Xfinity branding on the side instead of Netgear. However, even that is being phased out in favor of their XB6 and XB7 for people that get 600mbps and higher.

If you are gonna buy your own equipment don't take a step backward and I highly encourage you to get a modem that is DOCSIS 3.1 capable. A good example is the SB8600 https://www.amazon.com/ARRIS-SURFboard-Approved-SB8200-Frustration/dp/B07DY16W2Z/ref=sr_1_4?crid=2JQPP44XOWGKZ&dchild=1&keywords=sb8600&qid=1595727582&s=electronics&sprefix=SB86%2Celectronics%2C133&sr=1-4

As far as a router try and budget for something that supports at least 802.11 AC(AKA Wifi 5). You can get really good ones for like $120-$180 range.

Lastly, I will just say that you really should get 100mbps internet in today's day in age(or better). The only people that should be rocking 25mbs are those that are on prepaid(in which case you don't rent) or those on internet essentials program for $10 a month. I say this because 25/3 is rough for anything outside of simple streaming and school work. That assumes one person. To give some perspective lets take a look at gaming for a sec. Your average PC game nowadays on Steam is running anywhere between 20-50 Gbs in size. Triple-A titles like Borderlands 3 are 100+. For that 20Gb game(or file in general) you are looking at waiting 2 hours about and that is assuming ideal conditions. A 100mb connection cuts that down to just 30 mins. That is a big difference in terms of performance for what amounts to a negligible difference in cost. As they say time is money and that time adds up fast. Cause lets also be real most people got other bandwidth-consuming tasks going on in the house like my PC downloading a game while I stream Netflix type a deal.

Sorry for the book I just strongly believe what your about to do is foolish and will come to bite you in the butt if you do decide to upgrade down the road