All I can suggest is to put counters in some of your routines. I would bet that some or many may be running multiple times during the control's creation. In my alpha image control, I noticed that the paint routine would be called 2 or 3 times during startup. So, I used some flags I set in some events, like UserControl_Show and UserControl_Resize for example. And in my UserControl_Paint event, I would only paint if the flags were set properly. Now that control only paints 1 time during startup. If I had 20 controls painting 3 times each, it would take 3x longer for all 20 of them to completely display.

You may be able to do something similar. But it is important to first know how many times some of your routines are running during startup: use counters & play with just 1 control, not many, until you figure out where the slow downs are.