input includes tax paid under rcm.first make the payment through e cash ledger then avail credit through e credit ledger.but since output tax doesnt include tax paid under rcm, input available on account of rcm can be used only against liability under rcm
you can easily take itc on rcm first you mentioned inwards supply as reverse charge in GSTR - 3B. if there is payable in that month you should pay rcm amount merge with total taxable liability there is no need to make separate challan for rcm after pyt you will easily take itc on that rcm amount