Well, at least for the regulators - your life support system - I want to have a working relationship with someone who is going to be servicing it for me. Many shops will let you demo various pieces of equipment before you buy. So, for something as high-priced as that and is going to keep me alive underwater, I would want a face-to-face relationship.
Not to say that online vendors are not reliable - and I shop online for quite a few things, this is one where I would want to see someone in person, talk about the advantages and disadvantages, etc. And, perhaps you could work out a rent-to-own deal, or something like it.
There is something to say for being able to try on a BC before you buy it, maybe demo several in the pool first.
It's likely that, if you buy top line equipment, you won't be buying another set for a long time - if you keep up with the yearly maintenance.
Cheers
Mike