Does size really matter? And other Topics

A resounding Yes!

I have picked up many machines for $5.00 or free because they changed the needle and now the machine won't pick up any stitches at all. Some will immediately advise that the timing is off, and that's an expensive fix. Sometimes, I know better.
There are tiny differences in different brands of needles. Organ, No-Name, Singer and Schmetz.
Location of the thread eye, length, distance of eye to point can vary with brand and with type of needle as well. If someone set up the timing with one particular brand and type - It may not work at all with a different type. Many learn this the hard way, believe me - I know.

Another job that doesn't need to be as hard as people make it is removing the machine from a cabinet. I have had many take the legs off the cabinet and bring the whole thing in the trunk. Bloody heavy! Also hard on the back.

  It may take up to a minute to remove a machine the easy way. Lift the machine up until you see the bottom. Look at the far side of the bottom - You'll see a screw head at each of the hinges.  Undo these and pull the machine off the hinge pins. Sometimes the pedal and plug are free already, sometimes you need to undo a screw or two to free them. It's that easy.

Like cheap thread? - No. Like inexpensive thread? - Yes.  Those that sew a lot know that fancy stitches are nice but they use a ton of thread. I test every stitch of every machine I service and that uses a huge amount of thread. I pick up 3 $40 spools of thread for $3, sometimes less.  I cruise Salvation Army, Value Village and the like - They usually have some spools of  thread in neat little plastic bags. Saves considerable overhead.