There’s a lot of great advice in this thread.
Agree with creating “fluid long term goals” that are realistic. I’d like to pay my mortgage off by X year, get PhD in something which engages me, enjoy day to day life. I think I’m going to be an older woman who does the whole “retreat circuit” during the year
I enjoy the journey towards those goals and that shapes my routine? I think that loose long term goals are good because then you focus on what you need to do to get there.
For finances, buy in “up and coming areas and rent a room out”. Living in a slightly grubby area won’t kill you - oddly enough I’ve lived in cheap areas and my chums who live in “posh” areas have had more burglaries and vandalism than me! Look for location location location. I can walk into town and art galleries and libraries in 5-20 minutes from my place.
Re job/finances etc I also think that a good/professional/enjoyable job can help with social connections etc? People gravitate towards those with similar backgrounds to themselves, and I’ve met older women who feel that they’ve fallen out of the social mainstream because they “just” work as a receptionist or in a shop - but they clearly did have opportunities to retrain but just didn’t choose to take them 
Also don’t take what people tell you you “ought” to be doing?
I mean if you don’t like Prosecco and cocktail nights out and random dating and travel then don’t feel you “have” to do them?
I became a mature student and in terms of social opportunities, confidence I’ve got far more out of it than spending a year whale watching or trekking Macha piccua before arriving back home with “nothing but memories” . I’ll have the opportunity to relocate for my PhD and that excites me and I can’t wait 
I agree with the pp about “activity based” friendships? I go to meditation, I walk, I eat out, I wild camp - but I do it through things like meet-up. Lots of solo people there.
Don’t go expecting to find your new best friends or confidantes - turn up, be nice, muck in (avoid the skeezy guys who try to pick every woman up
) don’t overshare, leave on time. Keep it light.
Emotional support: everyone needs this, even married people. Loneliness and isolation and feeling like you’re not doing stuff right is the human condition to a certain extent!
Of course if it’s spilling into depression take professional help, but an attitude of “this too will pass” and just leaning into the emotions rather than thinking “if I got married this would not happen” can be helpful.
Don’t hang out with people who are obsessed with dating/defining themselves as “singletons vs the rest of society”/people who aren’t emotionally sorted themselves?
Better doing an overtime shift and watching a comedy episode than hanging out with weird mopey Helen because you feel you’ve got no other choice.
It’s quite easy as a woman solo to end up feeling like you’re expected to be support staff for others - put your energy into getting rid of that mortgage or language classes.