"So standard threading on the freewheel would mean that I can attach a track cog on to the rear hub with relative ease, correct?"

Yes, but backpedaling will loosen it, so add a bottom bracket lockring on top of it to keep it snug, and install a brake, naturally.

"Also, I think sheldon brown sells swiss bottom brackets and spindels for about $100. I would like to try to avoid this at all costs, but if I was to buy a new crank and chainring, would I need to replace the entire bottom bracket? "

Probably not. You would space / dish the rear wheel to mate up with whatever front-end arrangement you decide on, old or new. See below...

"So this is the way I see it for a cheap conversion if the bottom bracket and rear wheel are intact, I would need to:
attach fixed cog to rear hub via lockring and adhesive

Yep


"...buy new chainring attach to existing crank or buy new crank and chainring (if it's french or swiss threaded bottom bracket, do I need to buy a compatible crank?)"

No - I say use what you have. Pick the big or small chainring, buy a set of single stack chainring bolts, and put the chainring on the inside or outside of the crank spider to suit the chainline as required. French vs English vs Swiss involves the threads in the BB shell only, not the spindle / crank assy.

"...buy new chain"

Sure.

"...remove gear shift levers on stem and brake levers"

Leave the brakes on for now.

"...new tires and tubes."

Couldn't hurt, but not necessary if they appear intact.

"...and then I'm set?
Again, this is the way I see it in my head, but it may not make any sense."


Let's see what the consensus says. I think that's it.