As to how many fate points get awarded, it depends on the story but I'm usually giving one out every 10-15 minutes. We're new to this, though, so we'll see if this is too many/little. If all else fails, I tend to track the pc fate points, so I make sure i start compelling if they get down to 1-2 points.  I tend to compel them into adventures, and whenever they can't find something to do... lol

The rpg books give no reference for how long a turn is for thaumaturgy, even when just talking about adding power to it each turn.  However, Dresden is able at a few different times to quickly chalk out a circle - we get the impression that it takes him less than a minute or so to do so. 

So it really depends on how long you are equating a combat action to: if you see a combat turn as 6-10 seconds, like most other games, then you could be looking at 6-8 actions to get  thaumaturgy spell off in a minute, which is plenty of time to get dead in. 

I'm kind of on the fence, here... I think it should be kept separate than evocation (not instant), but that 5 minutes is way too long to really represent what Dresden does. Then again, whatever you choose will also represent how long it takes him to make a potion, which always takes Dresden hours... so a perfect representation is impossible.

or in two rounds if you used a previous exchange for setting up (and that'd create a taggable aspect to use when casting, pretty much guaranteeing success).

Because I like thaumaturgy remaining separate from evocation, this is similar to what I go with (and what we see harry do in the books a lot).  One round to scribe a circle, one round to cast.  We handle the taggable aspect by calling the circle a Lore declaration, since I give it  a difficulty of +1 and all of our casters would have a really hard time failing that roll.  I'm not really sure if this is supported by the rules (which seem to give little indication as to what "casting without preparation" means), but it's supported by Harry.

Sure, it could be 2 scenes.  Remember that a "scene" is simply an arbitrary unit of time, similar to white wolf's scenes, and is meant to designate something like "from tv commercial to tv commercial".  Any heavy action show will almost always end up cutting in the middle of a battle, or right after a reveal (the monster got TALLER, oooooh), or wherever they are at that particular 8 minute mark.  One "scene" was the events preceding the battle up until right before the "end boss", who warranted his own segment. Even one duel can be 2 scenes... just where ever the action naturally breaks (as in, they both fall through the floor to the lower level).

The game really plays like this, too... stress boxes come back between scenes (we see our hero thrown through windows, into trees, ect), but the consequences (the ubiquitous eye-brow scratch, the twisted ankle) remain. Ever notice how the hero should be way, way more beat up than he really is, but instead he's just got 2-3 really noticeable ouchies and some dirt smears?

In their explanation of why the game took forever, evil hat specifically mentions that spellcasting took a lot of work and playtesting to get right. Until I am really, really confident in my spell-fu, I think I will just opt for more scenes instead of adding house rules.