Yes, no replacement for displacement

Unless you’re building a budget towing rig, no. V8 can make as much power as a v10, more reliable, parts at every junkyard and local auto store, easier to tune, easier to fit in engine bay. Unless you have more money than you need and have a specific v10 that you have your heart set on for some niche reason, then just no.

Generally, I think, no. But that’s really not useful information.

Actually, it depends on what these engines are and what they will be used for.

I say V-12 or go home