Am I still eligible for hair restoration surgery?

It's difficult to say without the benefit of a formal evaluation. For hair regrowth, I suggest the following to my patients:
Start Theradome now (see link) and in office PRP/acell. You need a formal evaluation to see what type of hair loss you may have. when you have hair loss its best to do a full hormonal workup for internal optimization plus scalp biopsies or scrapings to rule out any stress related, inflammatory, autoimmune or infectious causes of hair loss. In general most people with early hair loss have telogen (stress related) and/or androgenetic (normal aging) and both can be treated with in office treatments like steroid injections, PRP/acell, Exosomes and at home treatments like oral medications, oral vitamins like Viviscal, topical exfoliating sprays like Restorsea, and weekly growth factors like anteagemd. See an expert for an evaluation. Best, Dr. Emer

What most people don't realize about hair transplant surgery (I used to do transplants), is that its not possible to transplant hairs as close together as they grow naturally. The best surgeons are likely to get you around 50-60% density compared to natural hair growth.
The best option (if you still have live hair follicles) is always to regrow your own natural hair. But what if you have already succumbed to surgery?
The good news is that if you went down the surgical route before you became bald and shiny is that you likely still have original hair follicles between the transplanted hairs. While the blood supply to these follicles will have been damaged by the surgery they are most likely still viable for regrowth. What this means is that if you get to them in time and work with a hair doctor expert in hair regrowth, you can regrow these hairs, healthy thick and strong to fill back in between your transplanted hairs.

I note you mentioned a couple of commercially available treatments. I'm sure you have heard of Keeps which is the generic FN+MN combination. There is a reason that company is called "Keeps" and not "Regrows". Regarding PRP, I'm really not sure how taking out the blood from your system which contains the molecules causing your hair loss, spinning them in a centrifuge to concentrate them and then injecting them back into your scalp blood supply is supposed to help the situation. But in any event if we assume that PRP acts as some kind of fertilizer to your hair follicles, you still have not stopped the problem which is causing your hairs to thin in the first place.

The only way to effectively treat or "cure" hair loss is to first get an accurate diagnosis of what is causing the problem via blood tests - which must be specialized blood tests to diagnose the causes of hair loss - not just whatever you get for your annual physical - and then treat the causes found. Only then can you introduce growth factors or other hair growth stimulants.

Without photos of the donor area, we cannot provide an accurate estimate.Nevertheless, 1800 grafts will rarely deplete your donor area, so I would suggest you consult a qualified hair restoration surgeon near you. He will examine your scalp and recommend the best treatment options for you.To slow down further hair loss and promote hair growth, medical therapy is always a wise choice.