The 100mm macro is a great lens. So +1 if you need a true macro.
Other ways to get close, that might work for you (and are cheaper than a macro) include extension tubes and closeup lenses. I have the Canon 500D closeup lens (an unfortunate name given the Rebel series), which is a high-quality dual-element lens that screws onto the front of your existing lens like a filter. It isn't as good as a true macro, but I've gotten very good results from it and it can turn a zoom into a pretty versatile close-focusing system. I find the closeup lens somewhat easier to use with a zoom vs extension tubes which will require a radical refocus when you zoom. I carry the 500D when space is tight and I can't carry the macro.
And, don't worry about lack of zooming and having to move the tripod. I've found over time that I have a good idea of the distance I need and get the tripod in the ballpark pretty easily. It'll come with practice.
I suspect most people with Arca-Swiss style heads have their clamps set where they can slide the camera left or right... I did something a little different. I don't like the clamp poking me in the face, or under the lens... I turned my clamp to the side. I use a generic square plate, I think the Kirk PZ-31. I can slide my camera forward and back a bit. I don't have the range of a true focus rail, but it works for me. I've thought about getting a slightly longer generic lens plate for more range.
I also bought a cheap lens collar for my 100mm on e-bay. About $10 USD. It works, but I won't call it fantastic. It makes verticals much easier without having to adjust the tripod as much. The downside is I have to disconnect the lens from the body to install/remove it.
