1. Yes, if you mean that you want to have a restore point that can be used to restore the whole VM. However if you want to have a single vbk file that contains everything then you should run synthetic full.
2. In your particular case incrementals do not include all the disks, neither does full. If combined they constitute the state when the machine had all disks present - some blocks are taken from vbk, others are taken from vib(s).
3. No, active full is not necessary. If you don't want to run synthetic full then you can do an incremental backup and use Backup Copy Job to create a single full without creating a new chain.