1) You can create a backup job and exclude unnecessary virtual disks from the processing, then you should be able to run FLR for the only drive.
2) Please keep in mind the backup size will be smaller than the source amount of data due to compression and deduplication applied. You can try a useful tool called "Restore point simulator
" for the storage planning.
If you are backing up SQL server by 3rd party or native tools you should switch Transaction logs to perform copy only