First off, congrats on the garage!
Wow, your footings are HUGE! I take it the natural soil is not very compact to require a footing like this (unless it is 3 stories tall). I also am surprised that the garage is not required to have some sort of engineering? Usually (west coast) all these questions are answered in the pre-engineered blue prints. Then once pre-engineered by private engineer..... the county in which you build also has a plan review process that another engineer reviews..... very overkill and expensive, but nothing seems to be falling down in high winds and earthquakes
In my experience a simple pour like yours can be done right from the concrete truck, but in more complex scenarios a pump is used. Dont forget to vibrate those footings to avoid pockets!
As for the height of concrete above grade at footings, I say higher the better.... get that plate level up high so your sheet rock does not get wet should you want to hose out. I also prefer a flat poor for the slab vs sloping as it works out great for work benches/cabinets/etc.
Hope this all makes sense and helps.
Jay