Mental Outlaw explains privacy in a simple way, there are legit service that have proved their good and bad relationship with their users.

Like proton and telegram will give out your IP address

Others may not

Just keep in mind it's a path, take your time.
Also, what may be important to you may not be for someone else and vice-versa, so look up and read up on threat modeling. This should probably be first on your list.

mini pc before the isp modem to filter dns

You mean after the modem and before your network? Then that solution is feasible, otherwise it really depends how The Net enters your domicile, odds are coax or fibre...
You may be able to flash your modem+router+switch black box the ISP provides, but YMMV on that one.
Regardless, you can set-up that mini pc inside your network as the authoritative DNS server to act as a DNS sinkhole — i.e. using a PiHole.

I have a pc w dual boot

Suggestion: linux-only with windows inside a virtual machine; other virtual machines can be used for self-hosting also.

backup data

Use 3-2-1 and make sure your backups are working.
Look into RAID and LVM or, better yet, ZFS.

dell optiplex

Lenovo Thinkpads tend to have a following in linuxland, but that's personal preference.

What am I missing? Where should I look?

Techlore has a series of videos on the topic and, along with the new oil, they have a weekly video on security and privacy. Non-tech-friendly. There are quite a few podcasts on these topics.

You can further your privacy by using frontends to common abusive sites (which i link to, sorry), such as invideous for youtube, etc.

A programming language is always interesting, linux is mostly based on C and it's not a bad start. I'll duck for cover now. Shell scripting — bash in particular — will get you a long way, as well a command-line text editor to change config files.

I get very few privacy vibes from this post. It seems like you are more interested in tinkering. Which is fine, but has very little to do with privacy directly.

Examples, you don't need to know how the IP stack works in order to have privacy. You know that a VPN is just a shifting of trust and something like the tor network would probably be better.

You mentioned flashing routers and DDWRT is open source router firmware and you should be able to add DNS blocks like a pi-hole or equivalent block list into that kind of software in order to stop ads and online tracking.

Pixel with GrapheneOS will have bigger impact for privacy... Buy used, refurb, etc

This is the resource I go to when I need to check something, and it should be excellent for learning more on some privacy topics.

https://www.privacyguides.org/en/

After that you might need to go find another resource for the specific technical topics. They have a discussion section, so you can ask for recommendations there?