At the end of the day I think it's socialising with those close to you, your 15 or so friends when you can and then the extended friends are those that are either spending time with you because their friends of a friend or something along the line, thus your spending time with them as well.
Another interesting point would be spending time with friends doing hobbies, for example I'll plan a hike and go with my friend because we both share that hobby, then on top of that is the option to bring my camera because it's a hobby I enjoy. But for less social hobbies I figure their better to be done during the week or when you don't have any plans for your spare time.
Introversion to me is more about how I recharge. If I am interacting with someone else, it takes energy to do so. If I was an extrovert, such an experience might replenish my energy. Instead, I recharge by being alone and solo activities.
So when I reference introversion, it was more in regards to how I recharge, not my level of social skills.
My wife seems to be quite good at making friends, because she invests a large % of her time and energy in socializing, and I feel like it is slightly less awkward for a female to invite female coworkers out to do something than it is for male coworkers (feel free to rebut me here). Fortunately, many of her friends have SO's that I've become friendly with, and we have a variety of "couple friends" we do group activities with where she also frequently hangs out with the female half of that equation 1:1.
I on the other hand have multiple hobbies, am working on teaching myself to code, and am constantly teaching myself new things (for example, I was brushing up on multivariable regression analysis at 1am in bed). I barely have time for this as it is without adding socialization to the mix, but I feel like I get more fulfillment out of my current approach. I've certainly learned more as a result.
I'm also an introvert. I can be very social and likable in the moment, but making new friends and the simple act of socializing is draining vs. my other solo activities which replenish my reserves.
Seriously, I'd love to know how people strike that balance and how they make new friends/maintain existing ones without constantly running on empty from the time and energy it takes to do so.