Tripod first. Think of it as a down payment for a macro rig. The 100L is nice, and the IS helps for larger subjects, but if you're planning on getting close to 1:1, the DOF gets thin, and you'll have to close down the aperture to extend it or focus stack; either of which will require longer exposures that are impossible to hand-hold.
+1 , Yes, Get the Best Tripods and the Best Head as your money can buy ( for the Biggest Lens + the Biggest Cameras that you have)---If you have not enough money to buy the Good Macro Lens---Just Buy the Extension first to use with your Lens that you already have---With Good Stable tripods and Self timer plus Mirror Up position = Great Macro Photos.
I disagree Buy the tripod that suits your need. If a cheap tripod suits you need use a cheep tripod that is stable. Buy the best glass you can get you hands on. Glass is the best investment you can make.
Second Live view with silent shutter mode two has no mirror slap at all. So Liveview offers much less shake than mirror lockup and is by far better for macro. In Liveview you can zoom into the area you want to focus on manual focus then zoom out hit DP preview to check the dept. Then hit the 10 second self-timer to take the picture and be sure of you results.