What format should I use to archive video issued from mini DV tapes?
I think that your choose are good.

H264 will be a bit huge in compare with H265, but will be supportable for more devices at this moment.

CRF you can get experimentally. Less CRF is better quality but bigger size of the file. 

Also you can use bitrate settings instead of CRF.
You can Focus on data from video recommendations for YouTube - https://support.google.com/youtube/answer/1722171?hl=en

I use approx 8Mbit/s for 1080p, 5Mbit/s for 720p and 1-2 Mbit/s for 480p.

If you need a good quality for video editing and all the videos were recorded on a good camera and you want to do color grading with your videos you can save them in Apple ProRes or Cinegy Daniel 2 or another losless or low compression codec.