Hi, Beth. First, fix the house foundation or framing. The cracks come from the house settling over the years. As this continues, the walls will crack some more. When you stop the movement, the cracking will stop.
Assuming that you have any budget left after that, then you can fix the walls. There are 2 good and easy ways to do this. I would not remove the plaster since it is really a big and dirty job unless your plaster has big "bubbles" on the surface. Your plaster was probably applied over wood lath strips that are now inside your walls. If your house has moved enough for the plaster that was forced between the lath strips to break in large areas, the walls will bubble as the loose plaster sags. Your best bet then is to have a pro come in and replace the plaster in those areas.
For cracking only, you do have a choice of applying a layer of drywall or facing with fiberglass. Before you start with drywall find and mark the stud locations using a stud finder. You can then apply 1/4" or 3/8" drywall to the walls by screwing it into the studs. Tape and sand the joints as you normally would with drywall. You can then prime and paint or paper. This is a pretty easy fix and the drywall will stand a little motion of the walls in the future if your joints have been properly taped. Depending on your particular moldings, you may or may not have to remove them to do this.
Newer technology is to use fiberglass fabric sheeting applied with special "paint". This is even easier than drywall and will stand more movement of the walls in the future. You do need to patch the plaster before you apply the fiberglass as any defects will show through to the new surface. On large cracks, dig out the old plaster and tape them like you would with drywall tape. You should not have to remove any moldings for this job.
We have used both the fiberglass and the drywall methods on my daughters 150 year old house and been satisfied with the results. The type and amount of cracking determined which method was used. We'll have to wait 50 years to see which holds up better.