First, understand what UKV&I defines as
switching.
In light of that definition:
1. No, your spouse cannot switch from PBS dependant to Tier 2 (General). He will need to return to his home country and apply for entry clearance as a Tier 2 (General) migrant based on a restricted CoS (for which an RLMT may be required unless he can find a job paying £155,300 or higher).
2. Dependant is not subject to cooling-off requirement, provided the dependant was not in UK as a Tier 2 migrant in the preceding 12 months.
3. Yes, you may switch from Tier 2 (ICT) to Tier 2 dependant.
4. Under current rules, yes.