Reef Tank DIY - For Dummies

[Dash]

Hi all,
I've been stalling on my tank upgrade because I'm feeling way out of my depth (see what I did there), and I've been hesitant to start a build thread here because you're all so intimidating to a newbie like me. Anyway, I thought perhaps others out there like me would be interested in something like this instead of the amazing tank builds you usually see here, so I'm taking the big leap forward.

My 75-gal tank will be 2 years old this November. I bought 2 green spotted puffers that the LFS told me were freshwater, and long story short, eventually ended up buying a used tank on CL and setting up a SW tank for them with the help of some nice folks on the Puffer Forum. I learned about live rock and mixing salt, and now I think I'm hooked. My current set-up is pretty medieval. All second-hand stuff except for the lights. No sump, hob Remora skimmer, SB Reef lights. I do a 16-gal water change once a month with buckets, and manually top off water twice a day. I do not use RODI water. (Please don't hate me).

My fish in order of when they were added: 2 green spotted puffers, YWG+shrimp pair, ocellaris clown pair, long nose hawkfish, mandarin, tail spot blenny, flame hawkfish.
Coral...a bit of everything including RBTAs (a lot of 'em), zoas, and some lps & sps.

I've been having a real blast thus far and luckily have all my original livestock, except for a lawnmower blenny who wouldn't eat and a long-nose hawkfish that jumped (RIP Lenny & Fergus).

However, I know my skimmer is barely able to keep up, I need to learn about dosing, and I'd like to set up a sump so I can have a refugium to increase pod population (for future girlfriend for my mandarin).

*note: apologies for crummy iphone pics



My immediate hurdle - I have no idea how to plumb this.