So if you're looking for long term standby, you're never going to beat CR123's (10 years is reasonable) or modern rechargeables such as Eneloops (i'm not certain offhand), which are extremely low self discharging, and you actually don't want to store 18650s at full capacity very long as it degrades them. Temperature matters a lot too, discharge rates at room temp are way lower than if it's at 110 degrees up in an attic or something, there's a reason a lot of people keep their batteries in the fridge (don't put them in the freezer though).
You're not going to lack power using an EDC size flashlight with anything bigger than AA size, which another option is a flashlight that can use everything, for instance AA eneloops, AA alkaline and 14500 Li-Ion are all the same size, and if the flashlight can handle the voltage, you can use what you've got on hand. Primary batteries (non-rechargeable) are great for long standby, and once an emergency does happen, you could run on them until you have time to get rechargeables into play. With a slightly larger than AA size, 2 CR123s is very close in size to 1 18650, and there are many flashlights that can use both (wrap the CR123s in paper while in a 18650 sized case to prevent rattling.)
Regarding mixing and matching multiple flashlights, two is one, and one is none. So yeah, I suggest having multiple, BUT I also suggest having them share batteries, it means more budget can go into having batteries. Make sure you put dates on the batteries too for inventory management purposes. Most EDC flashlights are beefy enough to survive a drop or two as well, so as long as there's no deliberate smashing, it should be fine.