TLDR: IT WORKED!!! It set great! It's quite sweet, but works well as jam. I don't really taste much grape though, so next time (ie next year) use a lot less water during the juicing part, so that the juice itself is less diluted.
Day 1:
Harvested 2.5 pounds of grapes from BH.
Put them into sink (stems/twigs and all) where covered them with water. Swooshed them around. Bad ones floated to the top. Put the good ones into the big but low pot, with a bunch of water to almost cover them. I think I put too much water, as my total at the end was more than it should have been for only 2.5 pounds of grapes (which was ~13 cups grapes with stems setc.)
Heated / simmered them while mashing them with the curvy potato mashes. The juice quickly came out. After ~10-12 minutes, stopped.
Let it cool a bit.
Then, used one of the mesh produce bags (with handles) to strain the juice out. Did a few go's at this to make sure no seeds/twigs in the juice.
Put the juice into mason jars -- ~7 cups total. Will refrigerate overnight, to see if that deals with the tartrate crystals issue (https://creativecanning.com/wild-grape-jelly and https://practicalselfreliance.com/grape-jelly/).
Day 2
Gently decanted the juice --- didn't really find any crystals I think, unless they were really mini as there was some sediment type of thing at the bottom but it didn't feel crystal-y.
4 cups juice + 4 cups sugar + 1 box Certo powdered pectin
Added 4 cups of juice and
1 box of powdered pectin (used Certo) to my big but short pot -- must use a big pot because it climbs up a lot when it gets boiling! Stirred to dissolve the pectin and brought the mixture to a
boil.
Allowed it to boil hard for one minute.
Then, added 4 cups sugar.
Brought it back to a boil. Boiled hard for one minute.
Removed from heat and spooned it into jars.
I put some of the jars into the fridge right away, the rest on the counter for a bit. They all set great!