That's pretty dependant on hardware. If you host small stuff , like a pihole or something, that can be done relatively cheaply, by using a micro-PC or a Raspberry Pi. Some services don't need to be always-on either, you only need stuff all the time if it's mission-critical, otherwise you can turn stuff on and off as necessary, for power-saving purposes. Self-hosting doesn't necessitate a huge rack and switches, or even your big gaming rig, my favorite thing to do with old laptops is throw Debian on it and find something I'd like to self-hosting from this list.
No, but putting a bunch of those services behind a reverse proxy would lower the amount of open ports. It would also have the side effect of making firewall configuration easier, since you don't need rules for all those ports anymore.
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