@nethead the slice gap closing radius needs to be set in Prusa Slicer. The instructions link from https://build.openflexure.org/openflexure-microscope/v7.0.0-beta1/high_res_microscope/test_your_printer.html in the blue (i) box in the middle of the page. This takes you to https://build.openflexure.org/openflexure-microscope/v7.0.0-beta1/set_slice_gap_closing_radius.html. You don’t need to print anything to check it, just look at the first layer in the sliced model of the main_body.stl and make sure that there is a small gap between the part and the brim.
I would strongly suggest that you build the V7 rather than V6, despite the fact that it is still labelled Beta. The high resolution version I linked to above is the one that you want and has all of the correct STLs in the print the parts page. RMS objectives are standard, but there are a couple of different options in the standards. The first is whether they are designed for an 160mm ‘tube length’ or are ‘infinite conjugate’. The standard Openflexure Microscope parts are designed for lenses specified for 160mm tube length. The next is the ‘par-focal distance’, which is often not stated in listings on cheaper lenses. The most usual is 45mm which is what you need here, but there are some with 35mm that will not fit the standard V7 microscope. Beyond that there are various lens qualities - a Plan Achromat is what you want here. There are a few Forum threads on objectives, for exampe Unsure if Objective lens will work - Request Help - OpenFlexure Forum and Sourcing non-printed parts - General - OpenFlexure Forum.
I checked and the LED array holder is actually in the Microscope full set of STLs, linked from the first blue (i) box in the customisations (https://build.openflexure.org/openflexure-microscope/v7.0.0-beta1/customisation.html. So you can just print that part. However I did not find any instructions or notes on how to use it. They must be somewhere, @samuelmcdermott might be able to help there.