You need to watch the report from your AM about the red card. If he says it was harsh, then there will be a chance to overturn it. If not, there is no point and constantly appealing will go against you if there are no strong grounds for the appeal.
From memory- go to the B team players you want and right click- select squad and then scroll to "make available for the first team" for the next game for 90 mins and he should be excluded from the B squad as soon as you hit continue.
The simple answer is to use your subs better and if you really need to make all 5 subs, then keep the last one till late in the game. Personally, I rarely use all the subs.
Historically there is usually only one more update in the new year for the end of the January transfer window- this happens around the end of February/beginning of March but there will not be any prior information until it is released. After that, there may be a minor update for any leagues that have a late transfer window.
This has been suggested before but SI has said multiple times that the option to spend the manager's salary is not in their thinking now or in the future.
There is no way that I know of where the game will change a PA that is set at the start of the save ( apart from as I said above ). You are using a third-party app that reads the database so there is no way of knowing whether this is affecting that player but it does make checking very difficult.