Does it really matter if your Digital Ocean droplets distro is x64 or x32?
Am I right to assume that x32 would be better for droplets with low ram like 1 gig?
Doesn't matter at all, 64 bit architecture allows the OS to use more than 4gb of ram. Up to that point makes no difference.
I would go with 64-bit in case you need to resize your droplet for more RAM in the future, if your NodeBB forum gets super popular. It's not really hurting anything to go with 64-bit anyway.