@Pablo_316, Mixing some forms of workloads can be beneficial for maximising resource usage - a regular VDI workload requires responsiveness (e.g. at least middling or better All-Flash) but often may not be taxing such infrastructure from a IOPS nor space perspective, adding other workloads to this to use the available resources may be a good option.
But do be aware of the hardware vs the workload requirements - if you go with something that will handle VDI easily but potentially won't meet the requirements of heavier workloads then this may be a problem, if you go with something heavier to accommodate the SQL boxes reasonably then maybe the spec cost ends up too high - mixing workloads with (potentially) very different requirements is always going be a balancing act and generally to ensure everything is fine with the resources provided, this tends to lean on the better-more-than-less side, thankfully this is getting cheaper and cheaper by the year and the price difference between top-tier and low-mid tier SSDs/NVMes is now lower than it has ever been.
While ROBO 25-VM license may be viable for the non-VDI workload I would advise contacting our sales team for cost of this vs 8-CPU vSAN license - there are also other things to consider here though e.g. vSAN Standard license covers All-Flash, vSAN Advanced or higher is required if you want to use RAID5, Deduplication&Compression etc., you need to know what you need/want in this cluster more specifically to make such choices.
While it is *likely* possible to combine a VDI-per-user license with a ROBO license I am not aware of the specifics of this (as Licensing is a separate SME not handled by VMware vSAN GS), but whether these 2 combined vs 8-CPU vSAN license is going to be more cost-effective is debatable - again sorry to add more "I'm not sures" (but you are asking this in vSAN sub-community), I would advise contacting sales/licensing team regarding whether 'vSAN for Desktop' per user offers are still eligible, but if these were used I would assume that anything not covered by these (e.g. non-VDI workloads) would require coverage by either per-CPU normal licensing or ROBO max-25-VM licensing.
If you are sure this isn't going to be expanded beyond 4 hosts then vCenter Foundation edition could be used but again unaware if Horizon has any issue/caveat with that (vSAN doesn't) - from the vSAN perspective the ESXi and vCenter version are irrelevant provided they allow creation and management of a cluster (and vSAN comes with free vDS capability regardless of whether the ESXi/vCenter have this included).
TL;DR: our licensing and/or sales teams know about the specifics of what you need and can currently acquire than the entirety of the internet and contacting them would be much advised.
