Looks like a math error: DNS should be -50% rather than -55%, since you took a +5% to the Spirit modifier. I hope you're using a spreadsheet or some character-creation software.
I can't comment on piling the DNS modifiers all together; that'll be Krys' call. All I can say is, man, taking a -50% power modifier is just asking
to be whacked with mundane or mystical countermeasures!
Since we're using multiplicative modifiers, you do not
add all enhancements and limitations together to get a single adjustment; instead, you have to do two bits of math. Let's use Healing as an example. First add together all your enhancements: Heals Self (+50%) and Cures Afflictions (+60%) yields a +110% increase. So the first thing we do is multiply Healing's base cost of 30 points by 2.1 (100% + 110%) to get 62. Now we add together all your limitations, including power modifiers: DNS (-50%) and Needs Attribute Roll (Will, -5%) sum to -55%. (Note that, including the power modifier, you're limited to a -80% maximum discount.) To get our final cost, we multiply the 62 points from the last step by 0.45 (100% - 55%) to get 27.9, which rounds up to 28 points as final cost. (Note that that's cheaper than the result you got using additive modifiers; more points, wahoo!)
If you have two abilities which you can't (or just don't plan to) use at the same time, it makes sense to buy them as Alternate Abilities. They need to have (all) power modifiers in common, and be explainable as different manifestations of the same basic "power." In your case, some obvious clusters would seem to be ( Medium and Oracle and See Invisible ) and ( Speak with Animals and Speak with Plants ). Depending on how much piling together you want to do, you could even bundle those two groups into a single package, and/or add Healing in if you can explain how it works using the same basic method.
Defining Alternate Abilities saves you points because all but the most expensive power only cost 1/5 as much. (The downsides is that all component powers go down if any one of them is disabled, and it takes a second to swap between different abilities in the same set.) In the case of the ( Medium and Oracle and See Invisible ), using your numbers, the final power would cost 24 (for Medium) plus 21/5=5 (for Oracle) plus 14/5=3 (for Detect Spirits) or 32 points, compared to 59 points for the unbundled powers. (For another, massive example of an alternate ability, see the thread describing Allison Vogel over in the "Young Superheroes" game I play in, which is the other offshoot of Silverthorne's original Spring Creek game).
Notice that you've over-limited Insubstantiality, by which I mean you've gone over the -80% cap. That's fine to do for flavor, but doesn't net you any extra points: you could strip out the Needs Attribute Roll and not change the cost at all.
Do Invisibility and Terror not also receive power-modifier discounts?
My rulebook isn't handy just at the moment, but I believe there's a pretty good example listed under the Accessibility limitation which might suggest a value for "Only while insubstantial."
Hope that helps!