Go to the move where you want to insert a variation and make an alternative. Then, a popup will open:
New variation will create a new variation (what you actually want).
Overwrite will overwrite the main move and all the next moves.
If you want to make a variation mainline, then right-click one of its moves → Upgrade variation.
Go to Options → Appearance → Movelist and under View uncheck "Show comments in the movelist". This should hide the engine thinking variations.
Alternatively, you can right-click in a move → Display → Comments.
This is a log file and can't be parsed. You can view the results in the GUI after the analysis has finished; then you can save the game as PGN (so that it can be parsed by Arena). You can do this by clicking PGN → Save current game in PGN format.
Scid vs Pc offers Speak-out-moves.
Assuming Version 4.21. (latest at the time of writing)
Go to Options Sounds
Under Move announcement, tick from the list what you want. For eg. Announce new moves will speak out loud the new moves on board.
For a basic installation, the Sounds folder must be chosen (on top of Move Announcement). For that, Scid offers a set ...