The BL460c G7, SB40c and D2200SB went end of service nearly five years ago, also ESXi 6.5 is now out of support - please don't run production workload on this kit.
To answer your questions;
1 - it'll be fine, presumably you're running those six SSDs in R10 or R6, so expect at least 500MBps of throughput.
2 - 'it depends' - it depends on how many vCPUs you assign and how busy they are - obviously you only have 12 full cores but if the VMs are not busy and you've not created unnecessarily large VMs then you should be able to run VMs totalling 24 x vCPUs, maybe more.
3 - Not much if anything - if your entire cacheable workset fits into 1GB then you'd be better just making sure you've given the VM enough memory to cache it in memory rather than let the disk controller do the heavy lifting.
4 - You only appear to have one, very old, underpowered, server - if so then any form of SAN will just add complexity for no real gain, in fact it'd probably be much slower than this DAS. There's nothing inherently bad in using DAS for a single server, the reason we use shared storage for multi-host clusters is to allow for vMotions/Storage vMotions and HA to work - you have to spend a decent amount of money to get DAS performance from a SAN/NAS.
This all feels like a home lab level of kit and if so then that's fine, but it's not production grade and I'd strongly advise against using it for that.
The best thing to do if you're serious about investing in production-grade kit is to look at the VMware Hardware Compatibility List (https://www.vmware.com/resources/compatibility/search.php) and stick to that.
