Make sure that the OLD will match the possibility of swapping to an IGH.
If you go with chain drive but think you might want to go belt later, you might want to include the necessary rear triangle differences if you change you mind later.
Small changes in gearing is not bad as long as there is enough space in the drop outs in the starting position. That is, changing the rear cog one tooth up or down should definitely be in range of most sliding drop outs. Maybe two teeth? I'm not sure but I imagine the BF folks could explain in detail. But my experience with belt drive on the Strida is that it's a meaningful upgrade.