Capital gain on property

I've sold a property for 3800000 and purchased a new flat for 1200000 in 2018. Plz clarify following doubts on LTCG

1) My purchase value of sold property is 10000 Rs in 1988. so now for calculation of indexed value of acquisition, should i take indexed value as base value for 2001 or FMV for cost of acquisition.

2) For capital gain exemption section 54e, should i take only purchase value of new flat or registration charges are added in the purchase value exemption for capital gain.

3) i've no income other than this capital gain, if my capital gain is less than 250000, should i pay tax and is it mandatory to file ITR.

please advise.