You can achieve more transparency using ARBG instead of the regular RGB function. For example, try to create a text object with background color rgb(63,72,204) versus one with color argb(100,63,72,204).
As far as applying the condition to the bar itself, use the + sign that's next to the expression, and set the color formula on the "Background Color" expression.
Well, there are a lot of ways to define "current" (e.g. last data date, previous month end, etc), but I'm assuming you mean literally the current (i.e. today). That would be something like: if(Month=month(today()),argb(100,63,72,204),rgb(63,72,204))