Hello, you can use bedtools makewindows -b <your narrowpeak files from macs2> -w 50 -s 25 > <output file> this will give you the sliding windows you want.

The Tn5 integration frequency is unclear, because you should have the fragments generated by the transposase "cutting" the genome, so I think you need 2 transposase reactions to generate one fragment. Could you elaborate on what you need?

Best, Dan