Two notes:

Eye relief is just the distance from the glass (on the eyepiece, where you look through) to your eyeball, when everything is in focus and you can see the whole field.

Long eye relief eyepieces generally have an eye relief of about 20mm. Anything under 10mm is uncomfortable for most people. I think 15 to 20 is about right.

I also wanted to comment on cleaning optical glass. For my eyepieces, I use a combination of alchohol and distilled water, and a cotton swab. Some people use the lenspen, and swear by it, but I'm more conservative (and I think it removed a speck of the coating on one of my eyepieces so I threw mine away.)

I never use compressed air on either a lens or a mirror, because there might be some gunk that comes out with the air. For air, I use one of those little blower bulbs you can get from a camera supply house.

I probably read the procedure I use in a book like Starware or the Backyard Astronomers' Guide.

For mirrors I use distilled water, a drop of dishwasher detergent, and a spritzer bottle to rinse the mirror really good. I use surgical cotten to lightly (no pressure) swab the mirror. Again, I got the procedures from books. However, I only need to clean my mirror every couple of years.