Best ways to combat slowdowns while creating full flash site?

I’m in the process of building a full flash site.
At the moment my site is just bits and pieces of different movieclips. I will definately load external .swf’s to my main movie to keep it’s size down and to make the site run smoother.

The site will have 24 fps (the site animation is supposed to move fast and smooth).
In order that the site will run smoothly I’d like some suggestions on how to avoid slowdowns.
My site will contain multiple movieclips (from different .swf files working together and displayed together at certain times and they contain motion tweens, alpha fades, masking and scrollbars containing long texts. The site will have photos, ie .Jpg/.Png, but thay are going to remain static.

Naturally I’d use a preloader for each .swf file used in the site.
What requires more CPU usage ? motion tweens or shape tweens ? Does frame by frame animation take less CPU usage ?

ANY suggestion would greatly be appreciated, Please do suggest !