I am planning to buy an iTouch and mac mini to test my game. I would like for it to run smoothly without any problems on ALL generations of iphone, itouch, and ipad. My main concern is the itouch/iphone 1st and 2nd gen - how powerful are they? I currently have a huge level built with over 6000 vertices (this is without characters, textures, and objects - I basically just have the terrain set up.) According to stats, I have 10 draw calls, 11.3k tris, and 6.2k verts. Would this run easily on all versions of the itouch/iphone? What vertex limit should I stay under for models? Which generation of an iTouch should I purchase for testing?
Sounds like you should go with at least iPhone 3G or 3Gs. I tested running an animated character with about 8,000 vertices on iPhone 4 and it appears to be limit. Even if your app is running so far on older devices, bear in mind that this leads to heavy energy sucking and thus to bad reviews and less revenue.
From a business point of view I would recommend to focus on newer models only. The installed base of 1st gen iPhones decreases and the people have to stay on older iOS versions. Keeping several versions, tons of preprocessor statement or heavy refactoring to use abstract factories costs you time and thus money as well.