Starter machine I can't recommend enough is the Singer 237 Early or Late style. ALL METAL GEARS! It can be fitted to a treadle table, or even upmotored. I'm seriously considering fitting it with a NEMA 23 or bigger Servo motor so I can fit a circuit to always stop upneedle or down needle based on a switch and also have a dead slow creep with maximum torque.
I'm going to upmotor my industrial Juki 5550 with a 3/4hp consew servo drive next big job we get with it.
When I met my wife, she had a Brother of mid 80's vintage. I brought in my 3 Singer's zig zags, and a Babylock serger. Since then we have acquired several vintage Singers, Necki's, and a Juki 5550 and a Juki MO-2516 serger (both industrial). I much prefer the Type 15 Bobins (The latch in kind) -- the drop in Type-66's tend to catch the thread and muck everything up.
I have just picked up a packet of 150/23 DBx1 needles and needle plate for the Juki industrial straight stitch to finish a scabbard I was making for As You Like It -- 3 layers of 2.5mm heavy leather. I kept breaking the 100/16 and 110/18 needles I had.
My early vintage Singer 237 I use with up to 130/21 needles and 24 layers of 4oz duck. Flat fell seam joints!! It will also run well off my inverter when we are on set or off caravanning. We have made our own tent out of 60" 4oz duck and this sping I had to replace the top and added square cut dags bound with 4oz duck instead of linen bias tape. Top is an 8' market umbrella. Sides are what I cut out and sewed up on my 237.
Robi