There's some guy on the TwistyPuzzles forum who made a simulator called pCubes. It simulates a lot of different puzzles including the Fisher Cube. It's under Cubic > 3x3x3 variants > Fisher Cube.
Use F U R U' R' F' to orient edges and Sune(R U R' U R U2 R') to permute edges. Then use an A-perm to permute corners. And then an intuitive corner orientation like:
-put first corner in URF position
-R' D' R D R' D' R
-adjust top layer so second corner is in URF position
-R' D R D' R' D R...
I recieved my ShengShou 6x6x6 last week, got a black one. But it's kind of sluggish and tight. Loosening the scews causes the outer edges to pop like crazy. To be honest, I'm a little disappointed. It might get better with a little breaking in, hopefully.
I'll order another one or two soon...
There is a piece that connects one corner piece to the core, remove that piece. That will make the two circles move freely. The two circles can not be turned independent of each other, without heavily modding the puzzle that is.
But why would you want to do this? It makes the puzzle way too...
Well, this is not possible, unless there is another flipped edge. There are no edges with invisible orientation and no duplicate pieces or anything, so like on a normal 3x3x3, one flipped edge is not possible. Pop it out and put it back in correctly.
No lookahead during cross stage.
Too many cube turns.
Slow PLL recognition.
AUF + cube turn before doing PLL.
I get way too frustrated when I get a bad time.
Timed solves make me way too nervous.
The last one is very problematic. When a friend times me without my knowledge, I'm about 2-3...
I think it's good to set goals for yourself, but they should be realistic. Otherwise you are going to get disappointed and frustrated. Trying to achieve a 15 sec average in two months is already enough of a challenge if you ask me.
But whatever you decide, good luck!!