To answer your Qs.
Primarily it's my only transport. I've not owned a car for about 20 years and been riding since I left home and I'm now 46. Secondarily It's an enjoyable pass time and I've met a lot of good friends through it and of course a few arseholes as well. I go to smaller bike rallies and camping events because I don't like crowds and over recent years I've started making my own bikes almost from scratch.
I 'got into it' as I couldn't afford a car for going to college, and even if I could there was no parking so I bought a junk 125cc for £50 and made it go again. This was long enough ago that the insurance for a 19 yo was not crippling.
So far I've never 'got out of it' but have been through phases of having sidecars which were mostly for my dogs benefit and also came in handy when I was dating a woman with a preteen child that loved it.
Mostly I ride alone these days, like to work, to the shops, to social events etc. I went through the club thing and even achieved rank in a sidepatch club if that means anything to any of you. But got out of that entire scene after I eventually realised that a reasonable sector of members had no paperwork for their bikes (hence they were shit to ride with as they couldnt go here, or there or on the motorway, or into town centers) and the other half obsessed over 'club life', and this was long before the SOA bullshit, and quite frankly there was more time devoted to talking and arguing about inter club politics and the friction (that did not exist) with other clubs than there was about actual riding and partying.
Only been in a few crashes, the worst was 2000 miles from home in Italy where I woke up in an ambulance and all I can say about that is read the local road rules for each country you go to, have good insurance, and never EVER ride tired. I walked away from that one. And it's probably worth saying I've not been in an accident for approx 15 years which is probably more luck than judgment.
I've commuted more miles on a bike than I care to think about, currently about 75 miles a day or approx 20000 miles a year. The thing I've learned about this is to save the heroics and speeding for another day when the roads are empty and you have a clear head. And if you can help yourself don't be a weekend warrior.
Apart from when I had a good job and bought a new 1200Bandit I've been riding generally what you'd call ratbikes, and even after I'd had the Bandit for 5 years and 100000 miles commuting that to was a ratbike.
This is my current bike, Been on the road like this for 5 years. Based on a BMW R80 frame and powered from a Kubota Z482 diesel engine. Top speed 70mph, cruising at 60-65mph, mpg between 125 and 150mpg (UK), and used every day and an annual mileage of approx 20000 miles. If you're wondering I have a custom build insurance policy.
My most fun bike was a BMW R100 with a Saluki sidcar. It was a beast and the steering was never quite balanced as it could be so for those few years my upper body strength was about the best it's ever been. My passenger was mostly a rottweiler who loved every moment of it.
If you're after advice...
Get good tuition.
Be reserved with speed, especially in heavy traffic.
Be observant.
Learn your stopping distances.
Get some experience, like go on a weekend road trip somewhere rather than your usual fave roads or afternoon run.
Consider getting a city commuter class bike and then upgrading to something shinier next year. You've no idea how much it costs to replace sports bike plastics or chrome parts, and even the experienced can fek those by dropping it whilst parking on an uneven road

Its also interesting that several people have gone the city commuter route into biking after chatting to me and then come back to me a couple of years later and thanked me because they really had no idea.
But most of all, keep the rubber side down
