Your choice comes down to a Series 2 or 3. Err on the side of stability or portability.
Few people downgrade from a Series 3 but many people find the need to upgrade some day, usually when long lens disease strikes.
I would go with a Series 3 unless you have compelling reasons to go with a Series 2.
A GT3542LS is very close to a Series 2 in weight (although a half pound heavier than prior versions). A Magica with Mountaineer + Markins Hub would get back to the old GT3541LS in weight, a Mountaineer in bulk (actually even less bulky than a Moutnaineer and far less bulky than a systematic) so is the ideal decision although the most expensive, as those things always are .
Edit: A Magica would weigh less than a GT3541LS, the Magica hub weighing less than the older Gitzo hubs.
You can evolve into a full Magica although it is cheaper to buy the kit.