By definition, preparation does not include execution.
It does when you have multi-phase plans. Lots of moving parts, mini-plans to execute the larger plan, making adjustments to account for complications. To use Ocean's 11 as an example, the plan itself is made very early on and relayed to Brad Pitt after the poker game. The lion's share of the movie is them then methodically executing that plan, much of it involving the prep for the actual heist, which is carried out in the film's climax.
No confusion involved. The latter is what CaW has been characterized as 'wanting,' the former is one way of delivering it.
"Blow through" has a nuance of rushing by, not giving something the usual amount of time and attention, which is really not appropriate here. In any style, be that CaW or CaS, or any other style one might suggest, the ideal is that something takes just as long or just as short a time as necessary and desired.
Well, it's either narrated by the DM (seems like the most reasonable option in any system, since no players are involved with the resolution, both sides are under the DMs control), handled with an ancillary wargamey sub-system, or it takes quite a lot of pointless dice-rolling to resolve.
Yes. The exact resolution system for this particular thing is unimportant. The important thing is where the decision points are.
D&D has always been pretty abstract that way, particularly the 1-minute rounds of 0e/1e and 'action economy' of 4e. Even 3e itterative and 5e multiple attacks arguably don't get down to individual blows - it's still not entirely plausible that 5 or 6 attack rolls represent /every/ blow in a six-second battle. You'd have to go to a system like GURPS to get that kind of granularity.
Yes, but the degree of abstractness varies from edition to edition. OD&D and Expert are probably the most abstract, 3e and 4e the most granular (it's very much my position that greater HP numbers of 3e and 4e did not make PCs and monsters more powerful, but rather allowed for greater granularity in combat). AD&D (1st and 2nd edition) fall in the middle, depending on how much wanted to use spell casting times, weapon speeds, and the like.
What about mercenary/soldier hirelings? I don't remember any rule addressing the XP issue in respect of them, either in D&D or AD&D, except perhaps the AD&D guidelines for discounting XP based on risk.
The hireling/henchman distinction in AD&D (or specialist/retainer distinction in Expert D&D) falls between those who provide logistic support (hirelings) and those who join the party (henchmen). Mercenary/soldier hirelings are meant to guard strongholds and camps, rather than invade the dungeon or provide protection in the wilderness. You could, certainly, take a man-at-arms or sergeant into the dungeon with you, but they would then perforce be part of the party as henchmen, and take a share of XP.