But depreciation *IS* part of your question.  Your third question asked about entering 1250 gain on the 4797.

If only straight-line depreciation was used, line 26 of Form 4797 is only zeros.  So other than reporting the sale on lines 20-24, nothing is entered about "1250 gain" on the 4797.

If accelerated depreciation was used, that changes that answer because the "additional depreciation" (depreciation in excess of straight line) is on line 26.