Have you fixed your banding issue? If not, I would suggest updating the firmware, then double checking that you have installed the full printer driver and not the AirPrint driver. The latter is not appropriate for higher quality printing and can lead to all kinds of problems. Banding issues have been reported elsewhere and have not been related directly to PL, but rather conflicting settings. Too many places where signals can get crossed.
Others have referenced Keith Cooper’s YouTube channel and Northlight Images web site, a treasure trove of useful information, with much content specific to the ET-8550. To help narrow the source of the problem, I would suggest downloading his sample printing test images. Print directly using Epson Print Layout without software image processing of any kind. The printer will often alert you to setting mismatches.
Regarding optimum print quality / detail, this is much dependent on the technical quality of the specific image and the specific paper and associated paper profiles. As @Joanna has commented there is nothing magical anymore about exact input image resolutions, whether 360 ppi or 720 ppi for Epson, or 300 ppi or 600 ppi for Canon. Keith Cooper has a nice video where he discusses all this (see below). In general, just send enough pixels to the ET-8550 printer and it will do all the needed calculations. How much is enough? For larger landscape prints on glossy to luster paper, Joanna’s 240 ppi may be all that is needed. Print and test for yourself.
If pixel peeping, or for smaller cityscapes or architectural prints, you might eek out some more detail with more image resolution. Despite what I wrote above, I do find 360 ppi to be a reasonable working target. I’ve occasionally seen some more detail at 720 ppi and higher resolutions, but I’ve also seen problems develop like ink micro-pooling or smearing which degrade the print. Do try upsizing a bit in something like Topaz Photo AI if more resolution is needed. There is an added benefit with Topaz PAI in that some AI sharpening can be applied as well.