Them's the ones, Garret. No.3 planes are a wee bit smaller and lighter than No. 4's (as you might expect!) You can find them for around £20 if you keep your eyes open. Snell and Atherton heel shaves are the only tool missing on the list for me but they do the same job as travishers.
I'd agree that the older your spoke shave or drawer knife, the better. Something to do with the way steel was forged in the old days makes the blades super hard.
Another good rule of thumb when selecting planes is: The thicker the blade the better. Older, wooden planes normally have thicker irons that sail though stock and are less likely to 'chatter' as you work the timber. If you're lucky enough to find a Clifton, Lie Neilsen or Veritas plane for less than a million dollars (you won't!) then snap it up!