Re: Bathtub - Replace or acrylic liner?
Without seeing the tub and surround for myself it's hard to say, however, from your description, the surround is leaking as well as the rusted through tub. My suspicion is that you're going to find wall damage and likely floor damage when the tub and surround are pulled. That being the case, it would be far better to remove the tub and surround, replace everything, and repair any damage not currently visible. Inserts are only feasible when the surfaces they are going over are in good condition, which yours are not.
Depending on what you replace the tub/surround with, and the extent you remodel the bathroom, this doesn't have to be an upsetting or massively inconvenient experience. It's all in the planning and the contractor you choose to do the work for you. If it were me, I'd demo only the tub and surround to determine the extent of the damage. From there a time-line can be created. It would also be very beneficial to have the new tub/surround on site before work begins.
Depending on the replacements you choose, the abilities of the tradesman you hire, and barring any peripheral damage, the tub and surround could be replaced in a day, and a new floor can go down in a few hours. Drywall repairs can continue with the bathroom in use and you never have to lose the use of your bathroom.
Now, if there is peripheral damage, as I suspect there is, you can stipulate that the toilet be reset at the end of each day, only leaving you without the tub for a day or two. The caveat here is whether or not the old unit can be removed and the new unit installed without having to demo a narrow doorway or remove the vanity. Other things, such as new tub type, surround type, etc., will affect the duration of the job.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!