There is really no standard scoring system. I think you need to decide two things based on your leaguemates.
1. What kind of player does your league want to have fantasy value?
Most leagues seem to prefer a balanced scoring system where big plays and tackles are weighted equally. If you're starting just 10 IDPs across the league in a system like that, you will (or should) see 10 linebackers starting every week. The best fantasy options will not include pass rushing OLBs or DEs or DBs except in the rarest of circumstances. If you're set on starting just one IDP and want a little variety and variability in who gets rostered and started, you'll want to increase the big play scoring (sacks and INTs) significantly.
Generally, a balanced system will award sacks and interceptions about 3.5x the points of a solo tackle while a big play system will up that ratio to 5:1 or more (sometimes as much as 8-10:1.
2. How valuable do you want that IDP position to be relative to the offensive positions?
Giving 0.5 pt per solo and 2 pt per big play may result in IDPs being irrelevant to the outcome of games. Giving 2pt per solo and 10-12 per big play may overweight them. Especially when you're using only one IDP a week. Though just using ten IDP starters will make for very little variability in your year-end rankings (i.e. IDP4 probably won't score much more than IDP10), there will be lots of week-to-week variability.
My suggestion:
Consider one IDP starter per position and give them reasonable and balanced value. That will allow the league to see that good tacklers and good big play options can both have value, that there's more to IDP strategy than picking the best linebacker and starting him every week and limit some of the weekly variability that can turn newbies off while allowing the owners who do a little more homework to do well.
Owners will still be tracking fewer players at each IDP position than the offensive positions with that setup -- that limited bench will likely allow just 12-15 players per IDP position rostered, leaving a deep waiver wire to pick through when needed so that guys aren't having to follow 50 players per position. It shouldn't be overwhelming.
Try a scoring system like the FBG default which will have a handful of players crack the top 75 overall and should entice the usage of a guy like DeMarcus Ware alongside Curtis Lofton and give reasonable value to a variety of DL and DBs.
Alternatively, consider a LB and a DL/DB lineup and the same scoring. Just two lineup slots but plenty of exposure to IDP concepts.
If either of those work, it should be relatively easy to expand rosters to include more IDPs if you like in the future.
And send 'em all here to get coached up and get involved in the world of IDP.
I'll bet most of them never want to go back if they get a taste of fun IDP can be.
