I don't know those sumps well enough to tell you what model it is, but just from the pics, I'd say you're doing well.
That sump appears to be decent sized, and technically speaking you can run a 75 on a 10 gallon sump, though clearly 20 or 40 gallons would give you more room to move, so to speak. Clean it up, use a mild acid like vinegar or critic acid for any stubborn mineral deposits, and I think you'll be in good shape. I'm guessing from the first pic you're missing a large (maybe 7") filter sock in the first chamber, or you can go with a filter "cup' loaded with filter floss, or no mechanical at all like some prefer. But I'm thinking you did well with this sump.
The skimmer in your third pic looks to me to be missing the pump. I do think there should be a pump coming in from the little pipe on the left at the bottom of the skimmer where that airline tube runs down and meets it. I don't know, but I would assume that pump could be replaced, and I do think that skimmer would go well with your sump. But, you could just as well go with a different skimmer, or no skimmer at all, as many successfully do.
The overflow in your 4th and 5th pic looks to be missing at least the "U" tube it needs to work. I'm also assuming that you have standard, rimmed 75 gallon tank, and likely you're not interested in trying to drill it. What I will say is that style of overflows do have some concerns attached, but that Eshopps you have in particular is one of the most trusted on the
market. Either replace the missing parts and go with it, or please know that it's not difficult at all to drill a tank, and with that in mind an overflow from Modular Marine would be a solid and arguably more reliable choice. Here's what I think you have, or very similar. You can see you're missing at least the one major "U" tube:
https://www.eshopps.com/product/pf-300/
I hope this helps and good luck!
