Is there a general rule of thumb you can apply here?
Chess isn't that easy.
The only applicable general rule that I can think of is that unmotivated exchanges will almost always be disadvantageous. Only exchange if you have something specific in mind.
No. It leads to different structures a Nimzo player should be familiar with, but it's not easy to be good at all of them : isolated queen's pawn, Carlsbad structure, hanging pawns, symmetrical center (or lack thereof), QGA center... It's not always possible to choose your structure from the get-go.
For instance after 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3 0-0 5. Bd3 d5 6. Nf3 c5 7. 0-0 Black can play dxc4 Bxc4 cxd4 exd4, or Nc6 allowing cxd5, or dxc4 Bxc4 Nc6, or with Nbd7 (with or without dxc4). It is a matter of taste but you also you need to know where you're going, which structure you understand and feel comfortable with.
That's why many players prefers to play c5 without d5 or b6 systems, it has more distinctive patterns and you don't need as much pawn structure knowledge.
In the Nimzo, I prefer the central Pawn structure pioneered by Huebner. Taken together with the exchange of the DSB, it makes a lot of sense.
Good advice already, just wanted to add, that's why for new players it's probably better to start with the QGD. After you learn about a few of the standard structures, the choices you have in the Nimzo will make more sense.
Or, as both people sort of suggested already, you can play Bxc3, d6 with e5 or c5 (or both) later. It's a principled and easy to navigate approach.
i play the nimzo. as black i will only release the tension because i am trying to head for the iqp positions where i could choose to play either nc6 or nbd7, and i know that white avoiding the iqp by taking with a piece on d4 only looks pretty but doesn't lead to anything substantial.
white can release the tension himself with either 7 dc or 7 cd in the nf3 bd3 line of the 4 e3 nimzo, but then his pieces will not be as well placed in the ensuing structures, in particular when black has the iqp, as there is not enough pressure against the iqp here.
i don't know of any general guidelines but the iqp and the hanging pawns are rather typical and so there are many games to illustrate the plans for both sides. you just have to be a bit more creative trying to win against the lame tries by white.
I have been trying out the Nimzo-Indian Defense for the black pieces over the past couple of months and had reasonable success with it (i would still consider myself a beginner) but there are many variations in which the c and d pawns can either exchange or just stay at c5 and d5 (facing white pawns on c4 and d4) and i am never sure what to do. Is there a general rule of thumb you can apply here?