As a rule of thumb, I would say a power costs 2 shifts per refresh cost. So, Aquatic 2 shifts, Hulking Size 4 shifts, Physical Immunity 16 shifts. Also, your Thaumaturgical shapeshifting seems to be trying to duplicate the Modular Abilities power (which has a 2 refresh surcharge) to I would also start with a base 4 shift complexity and then add the cost of the other stuff onto that.
I'll propose an Transformation-System based on Refresh (because I find it simpler and faster).
As basis I'll take the 2 shifts per refresh cost from biff_dyskolos.
When you (Self-)Transform into another thing you loose all your Powers and Stunts.Unless you buy them back into the Ritual.
The basic difficulty for transforming is based on the True Shapeshift Power (-4 Refresh = 8 Shifts)
(Reason, while one Ritual can only change you into one form, you can have multiple Rituals. Thats True Shapeshift.)
Since you may want to end the spell before sunrise, we add another shift.
So the basic Self-Transforming spell is an Complexity Ritual 9.
So lets say our Wizards want to transform into an Wolf. With the Lvl. 9 Ritual he can take the form off an Wolf, but he is unfamiliar with the body.
He incorporates another Power into the Ritual: Beast Change for the Skill Shuffle (Demonic Co-Pilot would work too?).
Thats another Refresh (Total of 5) or 2 Shifts of Power. = Complexity of 11
After an Encounter with an Hellhound our Wizards want to change into one.
A Hellhound is an -7 Refresh creature with the -4 from True Shapechange that would be -11. To much for our Submerged Wizard (10 Refresh Total, max. -9 Refresh)
He researches further and cuts the Pack Instinct out and the Stunt Unflappable (Presence), that would bring the Refresh to -9, but then he realises he needs still the Beast Change Power...
He cuts the other Stunt since he overlaps a little with Echoes of the Beast.
Complexity of the Ritual (9*2)+1 = 19
Later in the Campaign after the Wizard got 7 new Refreshes he bought True ShapeChange (-4) and the Modular Abilities (-3).
So he can Shapechange into an Wolf on the fly (with all his Powers intact), but anything more complicated (like an bird) he needs still to cast an Ritual.
He could change into an Bird with allmost all his Powers intact with an Ritual.
Example:
-3 Evocation
-3 Thaumaturgy
-1 Wizards Sight
-2 Refinement
-1 Diminuitive Size
-1 Wings
-1 Beast Change
-4 True Shapechange
-----------------------
-16
He could'nt use his True Shapechange, because this is the Ritual Version. He would need to end the spell first.
The Complexity of the Ritual would be (16*2)+1 = 33
With two more Refresh spent on Modular Abilities he wouldn't need the Ritual (And it would be
much faster).
IMHO with this you could play an Junior Wizards who grows into an Powerfull Shapechanger.
It's flexible, but you are at least 4 Refresh points behind the Specialist.
I like it so far... Opinions?
You could allow the Wizard to go over his refresh, with the temporary Power rule on page 92 YS.
Not shure about that...