My Metro 6/1 takes about 4.5 quarts. It has a single sloped sump with the dipper traveling within half an inch of the bottom; there's no place for gunk to settle to in these units.
I have one of Dave's hollow dippers. I noticed a bit more oil consumption when I switched to that when the engine was young, running the oil level at 1.5" depth on the dipper. I had previously run the stock dipper turned edgewise to the oil. Oil consumption did slow as the oil level went down. By about 1000 hrs of run time I didn't see a big change in oil consumption rate as the oil level lowered. I now start at about 1" of depth on the dipper, and add about 1/2 a quart of oil in 200 hrs of run time.
I have low/high oil auto shut down via a float/magnet in a sight tube that connects to the former drain hole and goes up to an angle nipple mounted near the top of the case. The visual sight line is from the top of the float, between the blue and yellow zip ties. Cheap magnetic reed switches are zip tied to the sight tube and close when the magnet rises or lowers too much. The shut down is set for oil level below 1/2" on the dipper when running. The picture shows just the low oil sensor, but now there are two.
I use a splash/gravity fed oil filter box inside the case just below the big door, inspired by Jack Beck's filter. I use cotton rags (socks, underwear) for media, with a 100 tpi copper screen at the bottom.
I do all my oil changes using a homemade propane tank- topsider to suck the oil out and then squirt it into waste oil containers. I open the big door so I can also change the filter media and swab out the bottom of the sump; so I don't have to disturb the oil sight tube plumbing to do an oil change.
Because of the oil filter on the door, the running oil level is lower than the fill level, and I had to adjust the visual and reed switches to accommodate this.