1. I think you should be able to look at the body to see if it has been drained of blood, although I think the original announcement should have stated if the body had been drained (I rarely have vampire caused deaths, and don't play since almost a year due to the raid equipment crash bug). I don't use the injustice system, so I can't tell you how to use it.
Question 2 is hard to understand. You might mean Z levels (the X and Y levels is horizontal, and the Z level is vertical). "Fortification" is a DF term meaning a wall segment with slits in it for firing missiles at enemies, but the context seems to indicate you just want to fortify your position. Wall segments automatically support each other when perpendicular to each other (i.e. not diagonal), and they can also be built on top of each other. However, you typically have to manage building on multi Z level projects to ensure things are built in an order that does not block access to building site.
An example: if you build a wall on flat ground, and then want to build another level on top of that, you can build a stair up along the middle of the wall (an Up stair, and then an Up/Down or Down stair on top of that, i.e. on the next higher Z level), and then you can designate the building of one wall segment at each end of the wall. Once a segment has been built, you can designate the next one in that direction, and so on. You have do do it that way to ensure the dorfs can walk on the lower wall to the building site. An alternative way to do it is to build 10 tile long bridges out from the upper stair in the above example (and further bridges out from those, if needed). That would allow you to designate the building of the upper level of the wall in one go, because the dorfs can now access each build site from the bridges (you'll still get cancellations you have to resume, because the morons will insist on deciding to build from standing on the wall, only to find that there's a wall segment there when they reach the place, and they're too stupid/lazy to move one step away to build from there). Once done you then dismantle the scaffolding (i.e. the bridges) in the reverse order from the one you built them in.
Note that building from bridges without a support from below requires support from the sides. You can designate building of the whole suspended wall, and dorfs will build, but as soon as a wall segment is finished and it doesn't have a finished segment to at least one side, it will drop and cause a cave-in.