How do you create drum tracks with fills?

[babydaddymusic]

I'm really diving into Reason in terms of songwriting. I love the simplicity of Dr. Octorex in terms of cycling through the 8 loop slots as a way to rough in a song.
I can think of a number of different ways to add variety to basic beats- meaning drum fills and variations but I'm curious how you all do this?

Here are the "materials" I have to work with.

An AKAI MPK 25 Mini with 8 drum pads

Reason drum kits RE
Kong
Redrum
Reason drum sequencer
Umpf both sets
Lots of loop loft refills

I'm also interested in how I can use blocks to do this as well.

The main things I hope to become really efficient at:

1) tapping in a basic beat first-
2) Adding let's say hi hat and such to that basic groove
3) Adding variations based on song structure- so intro, verse 1, chorus 1, etc...
4) Refining with fills and special trinkets

How do you guys do this?