I know your dilemma!! I have a Bernina which I love but refuse to lug up and down stairs and into the car. It's heavy but I'm more worried about it getting knocked or damaged ( they're not cheap).
I bought a fairly basic Janome which was fine but after the Bernina it just wasn't the same - advantage was I really didn't care if it was bounced about. I eventually found an Elna Lotus - quality engineering like the Bernina and really portable - no 1/4" foot so I used electrical tape.

I agree that the 37, without the edge is better and more versatile than the 57. You can always add a stack of post it notes or electrical tape to the bed to act as a guide! You might want to check your model to see if you need 37D rather than just 37 - the top of the foot has a cup shape to the right. Have fun with the quilting!

Glad you liked the Jalie site. Another one to look at is Fehrtrade.com.
Very old Singers (mainly straight stitch only) are very good but really heavy. I wouldn't touch a plastic Singer even if I was paid.
If you buy second hand I suggest you do it locally and test it yourself with your own material, even if buying from a shop. Don't begin to think about descriptions that say "no foot pedal or power cable" or "I've no idea if it works as I don't sew".
If you buy a new overlocker please try and get some tuition on threading and set up adjustments as 4 threads are a bit more involved than just 2.
No need to buy 4 cones of every colour either. Mid grey and mid beige/taupe/fawn blend in well so you only have to match thread to fabric in the left most needle and a standard reel will be fine. If you will use a lot of very pale fabric you might need cream cones as well.
You have probably already found out but try not to pin knit fabric as it causes holes which ladder. Use small bulldog clips or hair clips that snap shut to hold edges when sewing and use weights when cutting out. If you have a charity shop nearby, get some knit garments to cut up and practise on rather than waste new fabric.
Let us know how you get on.

Welcome to TSP. This is a really friendly and helpful place to be - never be afraid to ask what you might think is a "silly" question. We are all still learning.
I do think a basic sewing machine should be your first machine and I agree that older second hand machines are much better value than modern, cheaper low end machines. Do you have a local sewing shop that sells, services and maybe runs classes? An older machine from a well established shop should have some warranty plus help and advice. You don't need tons of stitches - a reliable straight stitch and reverse, zig zag, 3 step zig zag and maybe a blind hem stitch with the appropriate foot. Be careful of using the stretch stitch, it works really well but is the devil to unpick   
I'm reluctant to recommend a Brother overlocker because my first one was the 1034 and it nearly put me off for life! I found it clunky, noisy and difficult to control - it was impossible to start slowly. It went back to the shop several times and back to Brother twice but because it 'worked' ie stitched they said it was fine. I have seen other 1034 that were OK so maybe I was unlucky. I eventually traded it in for a basic Juki - love at first stitch!
You have obviously done lots of research so keep us posted and keep asking. Hopefully someone on here that knows your area can recommend some reliable retailers that can help

Good for you with the weight loss. I have done this alteration for my daughter and managed to keep the waistband on at the front. The trousers were RTW and I couldn't be sure how the band and fly had been joined.
I unpicked from the back to just in front of the side seams. I adjusted the seams to fit and took most in at the back. To get the waistband to fit again I cut and joined it centre back (lots of men's trousers have a joined waistband).
If you alter the crotch curve do it in small stages as it seems to go from baggy to far too tight very quickly. You can reduce a little back leg bagginess by increasing the inseam from the back leg only.
If you toile a smaller pattern size you could use that to alter the pair you haven't worn, but it would mean unpicking all the pieces first and re-cutting.
Maybe try adjusting the pair you like least and see how it goes?!

I am also a Bernina fan. I just love the way they sound and the stitch quality.
My first was an 830 Record - I had gone to the shop to buy a new Janome and saw it on the bench. I just had to try it, just so I could say I had sewn on a Bernina!! I did try new Janomes as planned but the ease of use and the samples I had made soon told me which was best.
Since then I got a good price on one of the last 550 QE. I had the course which was mediocre and they could not help with an issue I was having with invisible zips. I spoke to David Drummond and one of his assistants called me back and talked me through what I needed to do.
Janomes do the job and do it well but for me Bernina just do it better!
Had a Brother overlocker which worked but I hated it's clunkiness and noise and the motor seemed reluctant to get going.
Sewing for me should be a pleasure and I want to use machines that help me do the job without fighting or causing stress.
I was told by an engineer that all computerised machines should be plugged in and switched on every month or there can be expensive problems

Try this - not the cheapest but they have most things

https://www.u-handbag.com/collections/metal-hardware

That is a beautiful machine and the colour is something else. Do hope the service doesn't reveal anything nasty. Good luck and enjoy. I always use a circuit breaker on vintage machines even if they have new wiring - my OH made me promise!