I hope this stays up. I do not represent the company.
I was just looking at Shapeways.com and they print gears, axles  for different Bachmann older locos.
Two motor 44 ton and second generation 44 ton and 70 ton as an example.
Go look.

Rich

To my knowledge, sound modules might been discontinued by Bachmann. I believe only Bachmann has used them. I could be wrong though. I have seen questions here and other forums.
Only SoundTraxx makes them for Bachmann.
The Bach-Man should have the real answer.
You could check ebay.

Rich

Does this happen when running or handling the loco?

Rich

You should do ok with a little practice.

Rich

Terry.
You will find the soldering station will be a worth while investment over time.
Many have and no filing of tips, ever.
I still have my old 90 watt soldering gun somewhere. I put a plated tip on it many years ago.

Rich

When I use to solder with the WLC-100 I used the wedge tip at 75 and the pointed tip at 50 but practice with scrap material fist is always best but I have soldering since about forty years and came up though the ranks you might say. I was soldering to code 100 HO rails with the wedge. 50 might be a little high for PC board work but practice makes perfect. I used a scratch brush from Micro Mark.

Rich

I have been using a Weller WLC-100 soldering station for some years with plated wedge tip and fine pointed plated tip. No filling needed. I use Cardas Quad Eutectic Silver solder from Amazon for many years.

Edit> What I liked about the Cards is that is went from liquid to solid faster than any other solder. It is used in high end audio devices last I read.
An Optivisor helped a lot. for close work.
Rich

I remember now. It was a Precision Scale Model with decoder in the NYC A running both A and B. 
NYC BLI A and B with TSU-1000 in the next A and B I put in. Matched three decoder with trimming.
Pulled my 45 Pacemaker freight at the club.
I could not afford the proper steamer that pulled the prototypical 90 car freight.
Even had the proper 40 ft caboose in brass.

Rich

Users could also ask at the Kalmbach  trains forum. I see many more questions, suggestions there about these locos.

Rich

I just looked at the diagram page. It all depends on you mechanical abilities.
You could email NWSL and ask them. They have helped me in the past with a motor selection. and gearbox constructions.

Rich

I do not recall ever seeing that here. Maybe someone will show it.
Good luck.

Rich

Some people use a CDU like a Circuitron Snapper.

Rich

Is this it? Holding the switch too long can burn out a coil. Many use a CDU.

https://www.bachmanntrains.com/home-usa/dwg/dwgs/HO__6_Turnouts_Instructions.pdf

Rich

It sounds like a wired turnout. Here is a link about how they are used. Not sure it is correct.

https://www.bachmanntrains.com/home-usa/dwg/dwgs/HO__6_Turnouts_Instructions.pdf

Rich

It has been a few years. I have the power cab and did it with three locos. I did ABBA. It was not a problem. Just do not remember any details. I did some trimming of the CV's as I recall. The first loco had a factory decoder for controlling the A and B units.

Rich.