...can you both Amp up and Increase Area ... at the same time?
Yes.
Not only that, you can also both Amp Up and Increase Area more than once for that big play,
You might want to house rule a limit to the total number of Adjustments you may make to a single spell.
Does the caster/gm have to keep track of net hits you get when first casting a spell
Since net hits are often used for the effect of the spell you normally need to keep track of it anyway.....
For example
* Hush gives targets the Silent (#) status (see p. 53), with the number equaling the net hits on the Sorcery + Magic test.
* The spellcaster rolls Sorcery + Magic; the net hits from the threshold of any Willpower + Intuition tests viewers must make to see through the illusion.
* Roll Sorcery + Magic and add net hits to the target’s Defense Rating.
* Roll Sorcery + Magic; for each hit, you can levitate 50 kilos worth of material or people.
* Physical Barrier builds a wall where you want it to be, with a Structure rating equal to (Magic + hits on a Sorcery + Magic test).
* .....
Net hits on your Dispelling attempt will cancel out (reduce) the original number of net hits.
And with it the strength of the current spell will also diminish.
This is working as intended.
c. Summoning - ... Is that correct? (I'm not sure if the spirit actually rolls in step 3 or if it's a set number)
Yes, it is correct that it is resolved as an Opposed Conjuring + Magic vs. (Force x 2) Test.
edit: slipped by MC. I need to learn to not post walls of text
