Minimalistic Repertoire

 The Lengfellner System is similar to an opening system invented by an amatuer chess player who writes under the pseudonym "Pafu".  Pafu has three oopening book that you can read for free on his webiste:  http://www.beginnersgame.com

The one that is similar to the Lengfellner is called The Defense Game.  Here are the basic moves for Black:  ...e6, ...d6,  ...Ne7, ...Nd7, ...Ng6, ...Be7, ...O-O.  After that, Black usually re-locates the QN to b6 or f6, and then plays the QB to d7.  I've had mediocre results (at best) with this system in blitz, but then I haven't studied it too much yet.

 I've read most of "Action Chess", and I think it's an excellent book.  I should point out that the book received a very poor review on http://www.jeremysilman.com.

I think that "Action Chess" provides an almost-complete repertoire for both White and Black that is usable at least up to 2000-level.  (My peak USCF rating was 2022.)

Purdy recommends the Colle System against 1...d5, and 2 c4 followed usually by 3 g3 against other defenses.

He recommends an unusual line of the Rubinstein Defense:  1 e4 e6  2 d4 d5  3 Nc3 (or 3 Nd2) de  4 Ne4 Be7.  (More common are 4...Nd7 and 4...Bd7 [the Fort Knox Variation].)

He recommends the Tartakower Defense against all openings EXCEPT 1 e4, the Colle System and the Stonewall Attack.

"Action Chess" is relatively short for a repertiore book, and as a result there's some important stuff that' s left out.  But, if you do a little homework after reading the book, you'll have a solid, reliable repertoire for both White and Black.

 After 1 d4 d5  2 Nf3 e6  3 e3 c5 we have a standard Colle position after 4 c3 and 5 Bd3.  Please support your claim that the Colle  is "put down" in this variation with some analysis.  Thanks.

I too use Purdy's recommendation for the French. Its merit is it matters not what White plays; 3. Nc3 or 3. Nd2. Black plays dxe. Then 4.Nxe4 Be7 5.Nf3 Nf6, the Purdy position. Fisher considered C.J.S. Purdy to be the best chess teacher. I recommend his book 'The Search for Chess Perfection II.' He teaches how to make good moves. forget about learning the opening variations, learn how to make good moves.

There is a cult regarding Purdy and his writings and I am a true Purdy fan. Silman's 'Reasses Your Chess' is great but basically a rewrite of Chess Perfection. Now Agaard's 'Excelling at Chess' again teaches how to think and make good chess moves. I recommend all three.

I'm not sure you can choose a "minmalistic" approach. The theory is somewhere and eventually someone is going to know it, you can't rely on them not. My trick is to ignore the theory : my preferred defences of Sicilian and Grunfeld are quite quite theory heavy but get along fine not knowing any of it.