It's been a while since I've looked at these, but IIRC the first decision to make is whether you prefer the Luminor or Radiomir style case:
Luminor - 44mm; WR 300m; crown protection device
Radiomir - 45mm; WR 100m; screw-down crown
Once that's decided, you have to choose the model. If you're looking at basic models then it's the Unitas 6497-based handwind movement with or without sub-seconds depending on the model, and with no date. These can be found in the "Historic Collection" on the Panerai website.
Luminor Base (no sub-seconds)
000 - aka "Base Logo" - Painted dial (i.e. the lume is painted onto the dial); solid caseback; polished case; OP logo on dial; no swans-neck regulator
112 - Sandwich dial (i.e. the dial has cut-outs for the indices and a layer of lume underneath); display caseback; polished case; swans-neck regulator
114 - As 112 but with white, painted dial
176 - As 112 but with brushed titanium case
219 - As 112 but with crown on left-hand side of case ("Destro" in Panerai parlance)
Luminor Marina (sub-seconds at 9)
005 - As 000 but with sub-seconds
111 - As 112 but with sub-seconds
113 - As 114 but with sub-seconds
177 - as 176 but with sub-seconds
210 - Sandwich dial; display caseback; polished case; swans-neck regulator; no sub-seconds
183 - aka "Black Seal" - as 210 but with sub-seconds
The other Radiomirs in the Historic Collection are either gold / ceramic cased and / or have more complex 8 day movements = much more expensive!
As for homages, nothing really compares to the original but there's plenty on Ebay or the Timefactors PRS-20 is a very nice Radiomir-style watch. MMs are still available (try Manbushijie - never used them but they have them on their site) or how about a Wanted ad here?
I hope this helps. You might also want to try the dedicated Panerai forum Paneristi.com but don't mention homages!.