Well, right now, I've allied with the *spoiler*, so I've got a total of 10 scientists. 2 of them are up to par with my soldiers in terms of combat ability, so they 'part-time' it in the labs. Otherwise, I have one lab full of experts in the field of research, and one lab which I tap for people to go out and build geosondes/excavation sites/etc or train. The main tenet though, is the lab full of experts. For example, let's say you're researching "Firearms", an Earth technology. This will go faster when one or more of your guys in the lab have "Earth Technology", Major is even better. So, whenever I research something, I reshuffle the lab/training guys to maximize the number of guys with training in its field working on it.
Unfortunately, I only have 9 engineers, so I pretty much have to have one of two workshops not full. This is usually the one that's producing non-essential stuff, like extra small-arms ammo and weapon accessories. Otherwise, same principles apply.
Also, the other thing that I will try on my next run through is to make sure that groups of four guys have similar training, and that I never have more than four guys with the same training. So, for example, four guys with Earth, Reticulan and Planetology training, and four guys with Medicine, Martian and whatever else.
As for the Blaster Bomb approach at Terror Sites, I agree - but only to a point. You are pretty safe in nuking the outside to smithereens in the first couple rounds without killing too many civilians. But if you wait too long this advantage evaporates as the civilians start to come out of the buildings to "investigate".
Of course, I don't think I've ever let the presence of a civilian or twenty near a sectopod stop me from nuking it anyway - yeah, I take a hit of 50 or 100 points per civilian, but unless I'm trying to play some sort of "save civilians" challenge, I could care less. On the harder difficulty levels, there are enough UFO recoveries/etc to compensate for the loss of a few hundred points of civilians...
I think the key thing is to not take the gameplay too literally. If you did, then it follows that the "Best of the Best" of the world are attacking the aliens without any of the tools available to the modern military (recon aircraft, air support, snipers, body armor and helmets, etc.), and yet have the ability to instantaneously disassemble and transport UFOs back to a base half a world away. Meanwhile, landed alien ships allow X-Com skyrangers to land within as little as a hundred feet of them without so much as a peep, and attempt to "terrorize" human cities with population in the millions using 10-15 aliens. Additionally, the aliens always descend into the suburbs, and limit their activities to a (roughly estimated) 1000-square-foot area, and finally, are unable to mount any sort of tactical coordination despite having achieved interstellar travel.
So, with that in mind, the scale would be fairly small. Maybe not as small as depicted in the game (again, "terrorizing" a major city with 15 guys?), but fairly small for the most part. When we're talking about assaulting/recovering a UFO with 10 guys on board, you're fine with a single skyranger. An alien base? Two or three. Terror site? The local army probably helps (I'm just glad they abstracted the negotiations part - "What do you mean we can't fly our guys over Turkish airspace?"). X-Com isn't a massed infantry charge unit, it's a spec-ops unit. In the beginning, you'd probably have a horrendous casualty rate per mission (I generally have about 20-30% of a squad dying on superhuman against an equal size force, and yes, that's a horrible casualty rate for a modern military force, especially given that X-Com is basically the best of the best of the spec-ops).
Also, contrary to game mechanics, beyond a certain point, throwing more scientists at a problem does not necessarily solve it faster, nor does throwing more engineers at aircraft construction make that go faster. This isn't a frigging assembly line factory in Kamchatka or whatever, it's a high-tech research and manufacturing facility. 250 people dissecting a single dinky little sectoid? Yeah, right. 200 guys working on making a single laser rifle? Please.
Anyway, out of all that rambling, I would say, over the course of AW-I, X-Com consists of under a thousand soldiers, and three times as much support staff. Additionally, I'm sure that many times more people than that are indirectly involved in helping X-Com (weapon manufacturers, the guys who buy sectoid corpses for $20k apiece...)
The aliens, of course throw much more material overall at the problem, but X-Com has the advantage of concentrating force in a specific area.