In terms of FSDO, yes there are still issues with that, but it's generally caused by the user not looking after their Luxe correctly. Each Luxe is a different beast and requires different settings and what not. But all Luxes possible FSDO issues for the most part can be solved by properly fitting your orings... This, and raising the dwell slightly will ensure you have no issues with FSDO even with the feather touch screw in. I for one prefer to have mine out because here in Canada spool valves are a bit harder to keep from having FSDO so I like to play it safe by having mine out and dwell around 12-14.
The marker doesn't require any tuning out of the box. Go shoot it, enjoy it and maybe after 10-20 cases, adjust the manifold screw a bit to lower kick or whatever you need and maybe drop the dwell a bit. It only gets smoother as the orings break in.
In regards to using a 68/4500, I use it and love it! I have longer arms but it's still fine as long as you are around 5'8" or so but either way, there shouldn't be any issues with a 68/4500 tank.
I generally lube the Luxe after every day of play, as you should do for most spool valve markers. They do in fact take a bit more maintenance time then most markers like the G6R, Ego 11 etc but that comes with the territory. Spool valve markers are known for taking more time to work on but with that being said, the easy out, tooless bolt system makes it really easy to work on. The reg doesn't need to be maintained till around 10-12 cases so no worrying about that for a while.
The Luxe battery can last for a long time, and you even get a spare when you buy new. Now I am not sure how long a charge will last but you could easily play a weekend long scenario and probably still be fine with the first battery.
Most markers do have break in periods but the Luxe will be a smooth and quiet shooter out of the box. It's just the way it is, but again it gets better the more the orings break in and cycle so expect even better results in the future!
With cold weather, the Luxe should be fine. If you are really that worried, if it's going to be a bad, cold, rainy day, up your dwell to notches and play. You could always get it sprung so there's less chance of any issues arising but you should be alright for the most part. As you saw maybe in Galveston, the luxes were able to perform flawlessly after getting soaked and in PSP Phoenix, it worked great in the heat as well. They are very tolerant markers as long as they are looked after and treated properly.
Hopefully this gives you a good idea on how the Luxes are. They are one of the smoothest, quietest, and best shooting markers out there. They are definitely a step up from the DM, but don't get me wrong. DM's shoot nice but you will be pleasantly surprised when you get a Luxe.
Just my 2 cents.