Hi Chris,
thanks for the detailed feedback. This is really appreciated!
The answer to #1, #2 and #3 would be no.
Pattern-follow (phrase-follow) is something I miss as well, along with the ability to play from a specific line (#6).
As it has been mentioned, there are specific reason this is not currently implemented, but I believe this is a transitional thing. It should be possible to follow progress while playing, as long as it’s a “preview playback” triggered by you, and not the host.
#4: I have not experienced this myself, but will def. keep an eye out for that message. I know how it’s supposed to work though: presets should never be overwritten, unless you explicitly decide to do so.
#5: Currently there is no “post-trigger” or “follow” actions for phrases, so you can’t queue them up like that. Also, I wouldn’t really want something that did that, and only that - there is a much bigger creative potential here: think randomly picked phrases, repeating phrases etc…
#6: This should be an easy one, I hope it makes it into the first update 
#7: CPU usage of course depends on the preset, but creating an additional instance does not have a dramatic impact on neither CPU or RAM, as any additional instances will share the resources allocated by the first one. I usually run half a dozen instances - as I like to explore the new workflow offered with Redux, compartmentalizing my xrni’s and reusing them across songs. On a reasonable powerful computer you should be able to run at least a dozen instances or more.
#8: Renoise instruments would only sound different if you are using non-default TPL, or working off a different base LPB and having DSP effects which are synced to this tempo. Ticks Per Line are usually 12 in Renoise, and this value is hard-coded in Redux. Same for LPB, which is always set to 4 (yes, you can specify different LPBs for phrases, but it does not, should not, affect the tempo of DSP effects).