A newbie to the IDP world....

Hey guys im a new to the fantasy world and am doing a a IDP league. 12 teams redraft
Starting roster looks like this
1QB, 2RB, 2WR, Flex
2DE, 1DT, 3LB, 2CB and 2S
Scoring looks like this
 
Passing Every 10 passing yards (PY10) 0.1  Each Pass Completed (PC) 0.1
Each Incomplete Pass (INC) -0.05  TD Pass (PTD) 3
Sacked (SK) -0.5  
 
Rushing Rushing Yards (RY) 0.1  TD Rush (RTD) 3
 
Receiving Receiving Yards (REY) 0.1  Every 5 receptions (REC5) 2
TD Reception (RETD) 3  
 
Miscellaneous Every 10 kickoff return yards (KR10) 0.1  Every 10 punt return yards (PR10) 0.1
Kickoff Return TD (KRTD) 3  Punt Return TD (PRTD) 3
Fumble Recovered for TD (FTD) 3  Total Fumbles Lost (FUML) -3
 
Kicking Each PAT Made (PAT) 0.1  Each PAT Missed (PATM) -5
FG Made (0-39 yards) (FG0) 1  FG Made (40-49 yards) (FG40) 2
FG Made (50+ yards) (FG50) 3  FG Missed (0-39 yards) (FGM0) -3
FG Missed (40-49 yards) (FGM40) -2  FG Missed (50+ yards) (FGM50) -1
 
Defensive Players Each Sack (SK) 3  Interception Return TD (INTTD) 4
Fumble Return TD (FRTD) 4  Blocked Punt or FG return for TD (BLKKRTD) 4
Blocked Punt, PAT or FG (BLKK) 3  Each Interception (INT) 3
Each Fumble Recovered (FR) 3  Each Fumble Forced (FF) 3
Each Safety (SF) 3  Assisted Tackles (TKA) 0.5
Solo Tackles (TKS) 1  Stuffs (SF) 1
Passes Defensed (PD) 2  
 
My question is when should I start drafting my defense of players?
Any help would be much apprecicated thanks

To me it looks like your scoring is set up to give IDP players a similar number of points to offensive players, which is great (I've never understood leagues that have IDP and then give them half the points).

Line backers are the running backs of IDP.  You for sure want a top 10 LB as your lead man and a second guy in the top 20 LB (although if you can snag two top 10 that's better).  The WHEN to choose them depends almost entirely on your draft.  Personally I would wait until I see someone grab a LB and then make sure to get one right after.  That being said I snagged the first LB in the 5th round last year (a lot of new players) because Patrick Willis was just too tempting to pass up at that point.  There are also LBs that emerge throughout the year to be solid options, so I wouldn't reach too far after your first two.

Defensive line is like TE.  The top few guys are valued highly, but after that you can wait.  I usually just wait until near the end to pick DL and then pick up guys off the waiver as they bust out or more importantly if they play a team that gives up a lot of sacks.  Match ups are very important for DL.  Again, if it gets to the 5th or 6th round and Justin Tuck (DE) or Suh (DT) are sitting there it might be too good to pass up.

Defensive backs are like kickers.  There's not a huge difference between a top guy and a decent guy and because they rely on interceptions for their big points it can be next to impossible to tell who the top guys will be from year to year.  Ya there are the usual guys near the top, but they're just not worth reaching for.  Grab one or two good guys in the second half of the draft and you'll be fine.  If you see a guy on waivers lighting it up, grab him.  Every year there are previously unheard of guys who rack up the points.  Sometimes it's because they're the weak spot in the secondary and the QB is targetting them.  Also don't be fooled into taking a big name DB too soon.  Guys like Troy Polamalu and Darrelle Revis are great real life players, but only average for fantasy football.

One more thing I would add to DE.  Look for guys who are classified as DE, but actually play OLB.  Happens quite a bit and the positional tag can vary depending on which website you use.  I snagged Tamba Hali in the second last round last year because he gets mediocre LB numbers, but was actually tagged as a DE.

Fact - Josh has some very good points. I would listen to him.
Fact - I'm in the same league as Josh and LB ar GOLD! Getting a couple of good LB early is crucial.
Fact - My team is consistently better than Josh and I kick his ass every year.
Fiction - Josh likes girls
Fact - The IDP Guru site is awesome!

Good luck this year Joshy! You're going to need it. Sucka!

DSC, You are a delusional impostor.  My wife would beg to differ with you on the second last point.

Who won the championship last year?  Who has never won? How come I always steam roll you in trades?  So many questions.

Hey Joshy, I'll confirm point #4 with your wife tonght when I see her.

Hey IDP Guru, what do you think of Cushing? I managed to get him from a loser in my keeper league for a couple of scrubs. Is he going to have bounce back year?

P.S. Flutie Rules!!!

I think Cushing will do well in Wade Phillips system. I see solid LB2+ value, if not low LB1 value depending on how well he adjusts to the SILB position and how the Texans utilize him on 3rd down passing situations.

DSC,
Are you still trying to justify trading away your season to get Cushing and handing the championship to me in the process? You don't need to ask my wife about point number 4 ... Just ask your mom.  Cushing will continue to be a big play teaser. Decent year long numbers, but all from a few big games.