In Start Fund offering which has a different cost structure than if one would set up their fund on their own, what is the smallest check size to accept? 25k was mentioned in the Start Fund call as an example, but is there a specific threshold for minimum check size in Start Fund?

In general, irrespective of if you're using a start fund structure or a traditional one, your minimum LP ticket should be $100k. The lower the tickets, the more challenging the LPs are to deal with... Small LPs are often more work then bigger LPs.

In a traditional fund, you can go as low as $50k, but you need to do this on a case by case basis because at this level, you're barely breaking even on this LP when you factor in your time comittment. With start fund, you can go as low as $25k.