The general rule of thumb for VLB 1.0 is:
25MHz - 3 cards
33MHz - 2 cards
40MHz - 1 card
50MHz - integrated onto the motherboard
Mind you this was was only generally speaking. Your actual mileage will depend more on the design of your motherboard. I believe VLB 2.0 improved things a fair bit in regards to how many cards you could use reliably, but the standard came out pretty late (95 ish) and pretty much nobody built anything around it.
I have never really bothered much with VLB for disk controllers, but people who did have nothing good to say of it. At the time VLB was popular, I doubt there were many drives that could really take advantage of it anyway. Keep in mind 1-2MB/sec was pretty typical of drives of the era, which ISA could keep up with quite well. Though later PATA drives are certainly one hell of a lot faster on VL bus, the lack of bus mastering kind of stinks. Best to go with a caching controller in that situation.
"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium