OP
I always encourage you and others to get into or back into R2R. Even though it is my lowest S/N format, some tape hiss: I and all my friends pick LP over CD and R2R over LP. My Pre-Recorded Tapes are my best source.
"I’m going to make recording of all of my vinyl that didn’t get released on cd or any other digital format."
I have to ask why?
I sold some, still have around 350 pre-recorded tapes, my best source. 60 years old, still sound terrific. Tapes made from tape masters (or copies of masters).
I have some R2Rs I bought that others recorded from their own or borrowed LPs. They are fun, but definitely a notch down from factory pre-recorded.
I have a few 10.5" reels that others made, a mixed bag. For me, it's too much work indexing to find a particular album/song, and you have to stand at the machine to find ___? I stick with 7" reels.
Your deck has to be in terrific shape/maintained to move/stop the weight of the larger reels full of tape.
I have a half dozen I recorded off FM live broadcasts, they sound better than the LP to tape copies and are otherwise unavailable. I wish I had done more of them.
as for cost, you could probably find very good condition replacement/backup LPs, buy them for less than what you will spend for tapes.
Also, putting wear on the heads to initially record, and subsequently play 'ok sounding' tapes made from LPs will have you looking to have the heads re-conditioned.
Speed: perhaps you will be using 15 IPS. You will double the amount of tape needed, and if copies from LP's, how much difference will the higher speed make? I don't know, I stick with 7-1/2 IPS.
I certainly don't mean to be a downer, just my thoughts on your project.