I think that a lot of guys that collect find a niche for a particular type of gun that really interests them and then build a collection of various types of the same rifle. The Mosin 91 variations are a good example. You could collect literally 100s of rifles in this category alone with all the Soviet, Finn, etc., varieties.
If you are like me and you want a variety, it gets harder, because you have to research each gun type to know what is good and what is not in each type of gun.
For rifles this is my list of what I either already have or or looking for. I try to find a really nice gun or a couple of guns in each category (matching numbers etc..), so it can get to be expensive and slow.
Mosin types: 91/30, PU Sniper, Finn, M38/44, etc.
M1 Garand
Mausers
- Yugo M48
- M24/47 and/or M24/52C
- CZ24
- Swedish 1896 and/or M38
- K98
- Argentine 1909, and/or M91
Swiss K31, K11, 1911, 96/11
SKS Chinese Yugo and Russian
Japanese Arisaka Type 99 and/or 38
Enfield 303 and Ishapore
You could easily add a bunch more to this list, but it gives you an idea of the more popular milsurp rifles out there. For a starter, I'd look for a Mosin or an SKS, because they are still some of the cheaper choices, and cheap and fun to shoot.