1) I'm guessing you are talking about new shares as a private placement. - if new shares are issued, you suggested 375m in new shares, then that is added to the value of the club as the money raised would immediately becomes an asset - so not a 1.7b value but now 2b. To buy that 25% will thus cost 500m.
2) Yup
3) Yup
The problem with option 1 is no individual is likely to invest 500m in a company where they have a minority say, the 75% that DL + ENIC still hold will maintain full control. You could sell the shares in blocks to Spurs fans and small investors, which is probably doable, then you give THFC an extra 500m to spend, but it would all be in the hands of the current board.