Yes, you can set ringtones for individual callers, and you can use music files as ringtones (according to the manual; I haven't tried this, and the manual doesn't specify file formats). You can download the full owner's manual
here.
The one durability issue I've seen reported on Verizon forums is that some people who have taken the phone out into freezing weather and come back inside have had the screen crack. That's a serious problem if you live where it gets cold, but can probably be managed by keeping the phone in an inside pocket, not a coat pocket, when you go out.
As for learning curve, that's hard to say. I've never owned an Android phone before, and I haven't found it difficult to learn this phone. But different folks will have different experiences with that.
As to usability, it has worked well for me. I bought it specifically for the slide-out keyboard, which I find quite functional, e.g., when typing messages or e-mails, or longer search terms on Google. It does add to the weight and bulk of the phone. When I bought it, the Verizon salesperson said that most customers tell him that after a couple of weeks they don't bother with the slide-out anymore. Not me; my fingers are not adept with the on-screen keyboard, and I only use it for typing a word or two, otherwise relying on the slider. Some users report issues with call quality, and it's probably not the greatest speaker you can get (I haven't had any problems). I have not had problems with the phone making network connections. I get good 4G connections when they're available, and I found it easy to set up the connection to my home wi-fi network, and when I need it to the phone connects to it very quickly. I needed some help from the Verizon store to connect the Bluetooth to the older Bluetooth system in my car, but it has worked reliably and easily since then.
Yeah, "bloatware".... That refers to Verizon's pre-installed apps on the phone, e.g., Google Maps, Backup Assistant, VZ Navigator, NFL, Slacker Radio, etc. Some are useful, most are not; of course, which one is which depends on individual preferences. What is definitely true of them all is that you cannot delete them from the phone, and many people have tried. You could probably get rid of them by "rooting" the phone, whatever that is, but I know nothing about that and therefore do not recommend it. What you can do is delete the shortcuts from your home screen, and in your apps screens you can create a folder and dump all the icons in there so they don't get in your way. They do not take up a problematic amount of space on the phone, from what I've seen.
Hope this is some help.