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1) Starting all of the stress levels at 4 (while keeping the same bonuses for skill i.e. +2 stress boxes and a consequence at max).
I suggest reading some of the older commentary on Spirit of the Century's (SotC) stress track. Dresden's stress tracks were shortened at least partially because of some of the issues run into while playing SotC. From memory, the biggest issue was the feel of combat - too long and too repetitive. However, Google's memory is almost certainly better than mine.
2) Allowing fate chips to be spend (invoking an appropriate aspect) to take an immediate extra action.
I'm wary of extra actions. Also, the issues you mention can be solved in different ways. Allow casting reflexive rotes, stunts for drawing and attacking (or just a Declaration), etc. Extra actions seems a very brute force solution.
3) Allow resources to be used to make declarations on the quality of the person's gear.
This isn't a house rule - you can make declarations on just about any fact, knowledge, or bit of scenery. Just takes GM and table buy-in.
4) Changing the balance/economy of Guessing/Declaring/Assessing. Guessing would become free (like tagging) and take no action but if you guess wrong the opponent may make an appropriate declaration against you. (e.g. Harry guesses the gang leader is a 'Reasonable Man' but instead ends up with his 'Guard Down' by trying to negotiate). Declaring stays the same, free action that requires a skill roll. Assessing takes an action (which may be supplemental) but you may ask for all aspects related to on particular situation. (i.e. I want all of his emotional aspects or all related to fighting).
What do you mean by "Guessing"? Guessing at an aspect doesn't cost anything by the book...trying to use it does. Whether the GM confirms or denies prior to use is up to him. I tend to default towards openness unless I have a reason to keep something secret. At least one of the designers has stated he's open about almost all aspects.
I was also considering using the idea of Persistent (P) aspects from strands of fate (basically aspect so important that they don't require a Fate Chip to invoke, and would apply to any Consequence over Minor and some significant scene aspects like Burning Building (P) or Pitch Black (P)) but I'm worried that would add too much record keeping for my players.
Check out Fred's blog on hazards - it may clear up some of the "It's On Fire!" aspect issues. As for persistent 'aspects', I'm tempted to specify mechanical advantages to clarify tactical choices. Not entirely happy with the book's default of "it's up to the GM to set appropriate modifiers". From experience, they can get lost in the mix of other aspects.