If you visit my blog you'll see that I have showed many examples for using SVGs. However their use is still limited and you'll not get the answers you want to have to your questions.
Q1 You can use a Theme color when editing a SVG in Captivate (I never use another color) but the problem is that you cannot define an object style for a SVG, which means the answer to this question is negative. This is particularly annoying when using SVG as a button, reason why it is still not my preferred button solution: http://blog.lilybiri.com/overvew-6-button-types
Q2 Similar. In reality I only use Copy/Paste Appearance to be able to move a text style (which doesn't exist in the Object Style Manager which has only object styles) from one item to another, before defining the object style. See: http://blog.lilybiri.com/using-copy-slash-paste-appearance-in-11-dot-5-0 Negative answer, and I perfectly understand the logic here: how will you transfer the appearance (style) of an SVG with 3 colors to another one with 5 colors?
Q3 The roundtripping with Illustrator (sorry I don't use InkScape) is not at the same level as with Photoshop. I still hope it will be improved in future releases. The answer is negative again. Beware: the possibility to edit colors in Captivate is also limited. Use it only for simple SVGs. In other circumstances I will use Illustrator for editing. AI has a pretty nice Export Assets feature.
Nevertheless, the main reason why I still appreciate SVGs is for two reasons:
crispness in all resolutions, makes them excellent for responsive projects
the unique feature that you can limit the clickable reason for a SVG used as button to the image instead of the surrounding bounding box; for that reason SVGs are excellent for games; beware: not perfect.