Sounds like you’ll just end up with an ender 6. Maybe you can use that firmware and parts list and build guide?

I’d go prusa mini at this price point. It’s a really reliable little machine, and easier to build than the MK3 and others. Enders are really not worth your time, trust me, I had one.

What things are you testing? If it’s really nothing to do with the way it looks cosmetically, then you will be fine with FDM. But for mockups for reviewers, you may want to just order them SLA’d from JLCPCB. I got a part made by them and the quality was phenomenal and it was super cheap and fast. It’s slower than printing it yourself, but the quality is worlds better and you would have to order hundreds and hundreds before it costs more than buying a printer.

For figures, and especially testing things that will compare to injection molding, going FDM is a really bad idea. It’s superior for engineering parts and rapid prototyping in basically all cases, but is has terrible dimensional accuracy by comparison, and it has a ton of trouble with thin features and overhanging shapes. This is mainly because the nozzle width is orders of magnitude wider than the pixels on a resin printer, so the slicer has to get very creative with dimensions to make complex models work at all. I am a huge FDM enthusiast, but this really isn’t the right place for it.

I’m a heavy parametric CAD user, so I’m not very knowledgeable on blender, but I do know a lot of people who use it for this sort of modeling. It does actually have some really good parametric CAD plugins for when you need mesh parts to work well with precise dimensions.

This can be caused by gantry misalignment/warping, or not registering the bed mesh properly. Also, maybe the bed is warped in some way that was in the middle of the test points, so maybe a finer mesh could fix this.