I've worked on Citizen M3, M4, L12, and for the last couple years have been clocking most of my time on an L20-XII with a bit of L12. I programmed myself out of work on the M3 and M4 for the most part
As with others I can only offer one perspective as I've not worked with Tsugami.
I'm in SoCal and Citizen's support is top notch. 99% of the time someone is there within 24 hours if an issue pops up. The only time I can think of bad response times is when a few of their techs were working out-of-state for a couple weeks. I don't know how the service is in the rest of the state. Minor issues usually only take a phone call or two to fix. As far as service costs, I can't help you there as that knowledge is above my pay grade.
Tooling is freely available, third party or otherwise. Utilis, kennametal, applitec, etco, ph horn, sandvik, genswiss, take your pick. We have and use them all. You are correct, tool setting is done by touching off on bar stock. I've never known any other way, but some kind of tool setter could possibly help. Either way, you're probably going to need to dial it in.
The B-axis on the L20 is quite versatile, I'm a fan. 135 degrees of total travel gives lots of options. It's stock oil lines leave much to be desired, but if you replace them (and their aluminum tubing that breaks off the second time you try to position it) you're good to go. I don't recommend thread whirling with the B-axis, it is possible but is not the most rigid of setups and running the exact same parts we see 50-60% of the insert life on the L20 versus the M3 that has a static-mount whirler replacing two of the live gang tools.
The newer models of L20 have one coolant pump and a separate pump for high pressure, both of which are significantly quieter than the pumps on older models. The flood coolant lines are kind of a pain in the rear, especially if you're doing B-axis work AND work with the sub-spindle tooling as you then have the two worst-case scenarios and there is maybe a 3" window to set all 6-8 coolant lines and not have them knocked around. The saving grace here is there are enough ports to get high pressure to every stick tool on the gang and even a couple of the live tools.
I use Esprit as well and while the post sometimes spits out many lines of strange-looking code (no, most tool paths do not need 5 digits after the decimal) it gets the job done. I've found that it is best for complex and asymmetric features. Recently I had a screw with a T20 torx head, the tool path Esprit gave me was massive. I simply made some geometry, took some coordinates and programmed my own hexalobe with G2/G3 and cutter comp. What had been who knows how many lines by Esprit was done in about 15 lines by hand.
I'll be happy to answer any other questions, if I can.