Lellinger’s “The ferns and fern-allies of Costa Rica, Panama, and the Choco” (Pteridologia 2A) is at https://www.biodiversitylibrary.org/bibliography/124533 but is also available in print from the American Fern Society at https://www.amerfernsoc.org/pteridologia
Sadly, Part 2B was never issued, so it is incomplete, but potentially allows species-level keying for what it does cover.
I can also recommend Lellinger’s multilingual glossary (Pteridologia 3; https://www.biodiversitylibrary.org/item/216418). It might help you with Flora Mesoamericana, which should have a complete (if slightly taxonomically dated) treatment of Central American ferns, and is available online (http://legacy.tropicos.org/Project/FM) but is written in Spanish.
I generally consider it a good day when I can get a Neotropical fern on iNaturalist down to genus, although some of my friends can regularly do better. It is often hard to pause and get good photos that show all the key characters for a given group. Most of the major families do have a pretty distinctive gestalt (e.g., the linear sori along veins of Asplenium, not paired as in Diplazium, the typical pinnatifid dissection of Blechnaceae, with linear sori and often dimorphic fronds, and so on) but one excellent trick when dealing with completely baffling material (if you can do it safely and with permission) is to pick a frond and see whether it has 2 vascular bundles in the petiole/leaf stalk/stipe or 2 + several smaller ones, which distinguishes between eupolypods II/Aspleniineae and eupolypods I/Polypodiineae. (Obviously there are ferns that are not eupolypods, but this covers a considerable amount of ground.) I will see if I can think of any other good high-value things to photograph for distinctive groups.
It’s hard to pick a common species because there are so many! Christella dentata is a rather fuzzy, alien fern which is widespread, particularly in somewhat disturbed areas. Pityrogrammas are lacy with colored farina beneath and also tend to show up in somewhat disturbed places and canopy gaps. For tree ferns, if you can get a frond, you need to look at the scales on the petiole (of the frond); an apical bristle on the scale distinguishes between Cyathea and Alsophila. For filmy ferns, try to find fertile material; usually Hymenophyllum has clamshell-shaped indusia and the trichomanoids have a cuplike indusium with projecting bristle bearing sporangia. There is lots of Nephrolepis; when the fronds are in decent condition, the tip is coiled up like a tiny fiddlehead. There are one zillion species of Elaphoglossum, which are fairly common; for that genus and Pleopeltis, macro closeups of the scales are super helpful.
Hope this gives you at least something to start thinking about. I spent a week in Costa Rica last year with the OTS Ferns & Lycophytes class, and it was extremely instructive and a most enjoyable experience. Don’t step on a terciopelo.