Some of your examples seem a little dubious. Just because the spikes create husks doesn't mean you are somehow prevented from making husks elsewhere, transporting them to the combat zone, and then airdropping them onto the battlefield. ME2 shows that the Collectors bring husks to Horizon with them and ME3 has a codex entry on Reaper transport ships being specifically used to move legions of husks from occupied planets to the frontlines. This makes more sense because since when does anyone train (or in this case create) their troops on the actual battlefield?
Thismay be a minor problem but it ME1 they did use these Dragon Tooth devices (and I don't know if that name is canon) and it had an influence on the overall atmosphere. There was an effort made to create these as opposed to just havin husks pop upwhenever this enemy type was needed in later games. While you can easily explain this away there is still the tiny elephant in the room. Where did the spikes go and why did they disappear?
Certainly not because the Reapers were on their way to becoming the good guys considering there were screaming humans that seemed to be decaying quickly and painfully.
Also why wouldn't the Reapers interrogate prisoners? If they have information you might want to talk to them and the Reapers surely have indoctrinated thralls that could do that.
What for? What information does an indivdual have that couldn't be found out by means of indoctrination and ... or taking over the galactic givernment and accessing all information available on the Citadel.
I suspect they interrogate for the most part because it is a common practice in shooter-like games with military missions. There modus operandi was established in ME1 ... then tossed out of the window without explanation in ME2 and 3. Sometimes they indoctrinate, sometimes they kill, sometimes they interrogate, sometimes they experiment. And it doesn't depend on the Reapers ultimate goal ... it depends on what sort of mission the devs/writers/producers they wanted Shepard to do next.