Migrating lab from vmware workstation to proxmox

Hello

I have a i7 box with 16gb ram and 2x160ssd currently running ubuntu x64 desktop+vmware workstation as test lab for different kinds of vms.
I want to migrate this box to Debian + PVE.
My questions are:
1. Can I use existing vmdk disks to proxmox or should I convert them to qcow format?
2. On ubuntu I have utilized linux raid for 2 ssd disks.Can I do the same with Debian + PVE?
3. Can I use nested vms inside proxmox so I can test hypervisors like esxi,hyperv etc?
4. Will I have any noticeable performance gain by doing this change?

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