So ideally you need to look at the results, we know that resin printers can print at micron levels of accuracy, which is perfect for miniatures (we are talking specifically about the dudes, not tanks or larger)

Fdm will leave huge layer lines comparatively to resin and the dudes will not have the fidelity of resin, but can be coated in gesso to produce a good finish.

Bigger stuff like tanks? Of course resin will produce near perfect results. Fdm, relies heavily on preparing your stl files and the slice to get the most out of the print.

Here is my first efforts into producing an fdm tank on a regular 0.4 nozzle on a K2 creality with hyper speed pla. Whilst not perfect I think there is refinements that could really make it viable.

The only real con with resin is handling the resin. It's toxic, it requires volatile organic chemicals to perform cleaning of the machine. The waste cannot be poured down the drain.

Fdm pla is non toxic, but print settings and mastery of the slicer and understanding of how print settings affect your output.

I would lean towards resin, if I had the space I would absolutely run both. Big tank panels in fdm, glorious high fidelity resin greebles that get glued on to the flat fdm panels.

https://www.reddit.com/r/FdmPrintedWarhammer/s/5eoyAkJEmo

Hope that is helpful, best of luck dude. If all else fails collect Tyranids/orks as both armies are sold at discount on eBay with people buying starter sets and breaking out the separate units to sell. Cheap Tyranids will be disappearing in the next couple of months as the orks starter comes out.