Allocating Non-Standard Memory Quantities to Virtual Machines [duplicate]

There's no downside. You can add what you need in terms of RAM. Same for CPUs. If you need 3 vCPU or 4 or 5, you can assign as required.

Some admins like to see multiples of 512 and 1024, but it really doesn't matter.

No, there are no advantages / disadvantage. Sysadmins tends to prefer the round size, I do.

I can build a very small linux system and give it 403 MB of ram, the system will allocate what it is needed for it to work. But, you will not find modules of ram of 403 MB, because everything works with the powers of 2. So simply round to what best fit your build.

I used to virtualize Windows and Linux OS's in my single esxi and gave Ubuntu 768MB and Windows 3328MB and it was good for both, 4GB in total. If I'd have it with less ram, I simply would lose it.