I have ran a IDP league for the past 6 years. Why more league do not do this is beyond me. Defensive teams really hold no merit with me.
But to answer your question... It is important to decide the number of defensive players and the starting requirements for each position.
Too many defensive players / starting positions up front will make the transition more difficult. I suggest 4 starting defensive players (figuring 8 starting on the offensive side 1QB, 2RB, 3WR, 1 TE, 1 K). I started with 1 DL, 1LB, 1DB with 1 flex. As your league gets more familiar with IDP you can increase or not.
Scoring recommendations:
1 pt per tackle. .5pt for assists
2 pts per sack
3 pts per turnover
6 pts per touchdown
Under this scoring system the highest average scores of any player last season were 10pts/game. This is quite comparible to a WR in most leagues running with a scoring system like you have.
Another recommendation is to decide up front about 2 way players how they can score. There are not that many of them, but they do exist. I ran into the problem a couple of years ago during the Christmas holiday break, during our fantasy semifinals when Urlacher lined up on special teams field goal, and it was a trick play for a TD to him. At that time we had no rule for this scenario, and it created alot of problems as his score changed the outcome of the playoffs.