No question about it - different customers shouldn't be on the same VLAN.
Am I correct in the understanding that you are basically operating a hosting environment and hosting your customer's servers? Note you can't legally do this without being on the VSPP and licensing accordingly.
If you want to reduce IP space, there's no reason you cannot allocate a customer, say, 10.0.0.0/28. However, hosting customers shouldn't have to plan their IP ranges around what you host. I should be able to come and buy a service, tell you I want it on 10.0.0.0, and not have you say "but that clashes with Customer A". This can be acheived easily with VRFs and if your firewalls are appropriate, they will support said VRF without you placing a new firewall in for each customer. A maximum supported VLANs of 200 only shows you have switches not appropriate for a hosting environment. People running hosting environments typically look to more enterprise level switches, and start worrying about VLAN limits at the 2000-4000 or so limits. This in turn, is typically worked around through the use of multiple clusters with vxVLAN communicating between them.
I know this is a lot of information - but you appear to be running an enterprise environment and treating it as though it was a small business.