Welcome! To answer your questions:
2. Dragon is not the most stable program, but for me it has not affected the stability of the rest of my computer. I would not worry about Dragon's extra processes taking up memory. However I do recommend deleting (or renaming) the DragonBar executable once you're done learning how to use Dragon, as there's a bug whereby the Dragonbar shows up whenever you hit Winkey to open the start menu so that the focus is stolen from the Start Menu (you don't need the Dragonbar really - everything it can do can be done from the tray icon instead). I have no input into whether Knowbrainer's tweaks PDF makes it work purchasing Dragon from them, however I have found most of their advice to be geared towards users who are less technical than typical users of Dragonfly; I recommend basing any purchase on "can I download the installer again later if I need it" (because for Nuance's website, you only have 3 months to download the installer later unless you pay for some kind of extended download).
3. I have not tried WSR, but when it comes to Dragon and Dragonfly, there are 2 input "mechanisms": the first is Dragonfly's, which uses Windows APIs (
PostMessage IIRC) to send keys - this works fine in essentially all IDEs and processes, with the following caveats:
* on non-Qwerty keyboard layouts you might need to do some tweaking (I got incorrect output with IIRC Key actions when I experimented with the Dvorak layout, although Text actions worked fine)
The second is Dragon's input sending. This works fine for elevated applications, but it gets further subdivided into applications which support "Select and Say" and those which do not. For the former, you can use nice commands like "go before <some words>" to move the cursor around etc; mainstream IDEs are basically never supported by this, but some people have hacks for making Notepad++ and similar lite-IDEs work with this (google "dragon notepad++ select say" or similar). For applications which are not supported, the default is to show the "dictation pad" (a little window which captures your spoken input and provides a buffer for editing and a command to copy-paste that into the application), but it is slow so I recommend turning it off entirely. Personally I satisfy that select & say functionality using
http://handsfreecoding.org/2018/12/27/enhanced-text-manipulation-using-accessibility-apis/ for short bits of text and
http://handsfreecoding.org/2015/08/30/avoid-the-dictation-box/ (except using
https://liquidninja.com/metapad/ instead of notepad, so I get multiple undos, always on top, and window transparency) for long bits of text.
Regarding incompatibilities/gotchas specifically, one annoying one that comes to mind is opening a large file in a select & say enabled application can cause Dragon to become unresponsive; under the covers I believe Dragon uses COM and other tricks to mirror the text from the application to its own buffer so that it knows what words are available, and for large inputs (e.g. 1MB file opened in notepad) it runs out of memory and as a result repeatedly writes a whole bunch of debugging data to its log files (also burning up your disk space) until you restart Dragon. So err, just don't do that. (Also fun fact, the log files themselves are set at 10MB and open in notepad by default themselves so you can imagine that being annoying to track down..)
Anyway, on the whole I highly recommend buying Dragon - most of its surrounding infrastructure ranges from buggy to average however its actual speech recognition accuracy and latency is currently unmatched, so if you're getting into this because you need to avoid use of hands and you're writing code for a living then IMO it's a no brainer to buy Dragon for use with Dragonfly (unless MacOS is your poison of choice, in which case I'd recommend
https://talonvoice.com w/ Dragon for Mac, though it's a little hard to buy the latter nowadays and when you do you need to make sure you patch it to the latest version - the Talon Slack is very helpful in figuring that stuff out though).
- Caspar