It could be a good idea to move more critical things to a different machine. It's often said that you shouldn't run your router and/or firewall on your main server, but I think there are also security reasons for that.

Or to move those to a low power consumption machine with cheaper hardwRe that are either more resource friendly, or very heavy but it's fine if they can only finish their task over a longer time.

Also, think about how could things go wrong. Have a second DNS and DHCP server (it's difficult to run a secondary DHCP besides the primary, maybe you don't need that), and some way you can reach the internet if the router or the firewall gets borked. That "way" does not need to be accessible at all times, but you should be able to switch it on when needed.
Don't forget to test that these are actually working after you have sweet them up.

Whatever you decide on, don't forget that you don't have to do everything at once. Don't let it overload you. Learning new tech takes time.