1) Probably. The L2D gives out 12 lumens on the low setting, but regulated. The Minimag is 15.2 lumens, but this will diminish very quickly, particularly on alkalines. It is likely after 10 minutes that the L2D will be brighter.
2)Multi-mode system is not that complicated. Keep the bezel untightened for the light to be in general mode. Then, click once to turn on it 'low', and then tap the switch lightly to bump it up to medium.
3)Yes, you can expect an excellent lifetime out of Eneloops. I am pretty sure the runtimes were conducted using freashly charged Sanyo 2700s. However, these have appalling self-discharge, so in real use, the Eneloops will last longer.
4)I would not recommend less expensive lights. The Fenix drivers are the most efficient around. Anything else will just disappoint.
5)You are actually quite sane. 123 powered lights are good where you use them infrequently, or you don't have to pay for the cells. However, high-performance cells such as Eneloops are king in the everyday usage world. I have actually retired my 123 powered lights in favour of rechargeable options.