I am very pleased about your interest in this plugin.
Otherwise it looks (because here are almost no reaction), that plugin is either complete shit or that it is completely perfect.
You've probably overlooked a warning that you must use MB version 2.1.4181 or later.
But this problem have you solved it.
1) allow now playing track to be added to custom playlist
I'm not sure, if there is any suitable method in MusicBee API for creating such action.
In addition, I do not know how you imagine it. What you mean by "custom playlist"?
How will it be decided to which playlist to be added to the track?
Can you please clarify this?
2) allow now playing track to skip by 5 sec , 10 sec, 20 sec, 30 sec etc..
Yes, I can add an action that will perform such work. However, it is very easy to do it already.
Here is an example of how to skip 10 seconds: