1- Yup.
2- Yup.
3- Iirc we can't get custom windows to save their size and location, so it'll have to be fixed in the center. And we definately can't make individual elements save their locs, so it'll all have to be pre-arranged according to your spec. (This is assuming it's a shoved-in addition and not a replacement to the target window.)
4- Yes, depending on how it's set up.
5- Assuming /GameData.Spells.Casting works properly.

6- k
7- Not unless it completely replaces the target window.
8/9- Well sure then.

But the TierIndicator and Info text would have to be there too, and I don't think it would be feasible to have it be switchable: You'd be stuck with the HUD as your target and implied windows. Also, you'd have to work in a place for both sets of buff icons.
Anyway, think about whether you want it as a replacement or an add-on, and whip up an image showing how you want everything laid out. If you decide you just want bars, just list the order you want them in (and be sure to tell me where to switch from left to right side

).
If replacement:
- If you want to move/resize in-game, you'll have to do so for both Target and Implied Target windows.
- Include target & implied target name locations in layout
- Include locations for both target & implied target buff icons in layout
If add-on:
- No icons
- No tier indicator, or Solo/Heroic/Epic text (But the relevant info is shown in the ProxyActor still, so no biggy)
- It won't be resizable in-game, so I'll need to know exactly how big you want it in pixels, both vertical and horizontal. (Current is 256x256)
Bed time then work time, so no rush.