I’d like to know what essential locos you would suggest for a small transition era freelance layout.
That depends on exactly how small. If you’re talking about a standard 4x8, than I’d say 2-4 locomotives. Personally, I’d have 1 medium size steam locomotives (2-8-2, 4-8-2, 4-8-4, etc.) and/or one or two road diesels (GP9, F3A and F3B, RS-1, etc.), and one switcher, whether it’s steam (0-6-0, 2-8-0, etc.) or diesel (S-1, GE 44-tonner, etc.), although I think diesel would be a little better. This is probably a little more than you’d actually need (not that there’s anything wrong with that [;)]), but this will give you a good variety of locomotives and plenty of motive power to work with.