I was thinking of buying a laptop with a 1tb hard drive and then buying a 60gb or 120gb ssd to use as a cache with the hard drive, replacing the optical drive.
1). Would this work?
2). What sort of performance gains am I likely to see?
A cache works well only if you can hold most of what you repeatedly use in the cache.
If you can do that, then you are better off by using that size cache as a ssd in the first place, Use the hard drive for lare storage files.
A laptop with included ssd is usually very expensive. I buy a laptop with the smallest & cheapest hard drive, intending to replace it with a suitable sized ssd. I more storage is needed, add a separate internal or external hard drive.
If you have extra ram, Samsung magician can use up to 1gb of it as a cache when accessing their evo and pro drives.