So, playing-wise, it's all sunshine and unicorns - the new ES-150 is really inspiring, and has made me play guitar so much more than would otherwise. It's great, and moreover, it's special.
That said, there are some practical concerns I hadn't really thought about, and I hope you may find them useful.
How many frets?
So it turns out I've been used to 20-22 frets my whole life. Since starting to play swing guitar, I'd been systematically been weening myself off of playing past the 15th fret, because, to my ears, it sounds exceedingly anachronistic. However, there were a couple keys, or a couple licks where I snuck past. However, I discovered while playing "China Boy" that where'd been expecting to be able to hit a high "C" at the 20th fret, that a vintage ES-150 only has 19 frets, so I couldn't resolve the it. There's a video and it's pretty funny to watch me leading up to where the note should have been and then finding it wasn't there. Oops.
Tuners have come along way
So, truth be told, the build quality of an ES-150 is more like an L50, and not that of an L5. It wasn't exactly the top of the line, and so the Grover Sta-Tites it came with weren't quite as good as the closed back tuners that came on L5's and other nice Gibsons. Moreover, tuners have come a long way since then, and gear ratios have gotten so much better. I've read that the original tuners are 12:1, which wouldn't surprise me - it can be a little annoying trying to get a string in tune when you can't quite get the tuner to sit in between too sharp and too flat. Since they were pretty common, there are direct drop in replacements with modern ratios. While I could've gone with Grovers with a pretty awesome 18:1 ratio, I took the advice of several good sources and went with Waverlys. While only being 16:1, I've seen too many sources to count that describe them as just the best tuners made. A historic instrument I plan on having for life seems like a good place to invest in the good stuff. I could've saved $100, but I think'll be worth it. They're on on the Fedex truck at moment, so we'll see how things turn out.
Do you realize how ill fitting most cases are?
Getting the original tweed/airplane stripe case was of course too good to be true, but the ES-150 came with a servicable standard hardshell case, usually known as "Canadian" cases. I was really surprised by how much wiggle room there was, and thus how much the guitar can bounce around inside the case. It wasn't until I flew the guitar to North Carolina using the Case Extreme and the hardshell case that I noticed how mediocre the fit of the hardshell was. While I've had 10 years of succesful travel with the Case Extreme, I was usually flying a guitar in a gig bag, or a hardshell that was designed for that guitar. I started looking at cases, and because of the "off-the-rack" nature of almost all cases, there's usually a significant amount of room. I guess that's fine for something fungible, but for something historic, that just won't do.
Flight cases are really, really expensive
So I started looking at proper, custom built flight cases. Holy crap are they expensive! Calton cases are basically the old-school, industry standard. However they are $1000 now, and they're really heavy. New cases from Karura and Hoffee are still $1000-$1200, but because they're using Carbon Fiber, they are a great deal lighter. All three are built to order based off extensive measurements of your guitar, so they will fit like a glove, but it may only be a one-trick pony. On the cheaper end, Hiscox's nicest case is a proper flight case, but has off-the-rack fitting. A newer entry, BAM from France, $700, uses a suspension padding system to customize the fit of the off-the-rack cases, but I noticed they try to sell you a $300 case cover, which makes it a flight case. So, is the $700 core case not sufficient? Again, given the historic nature of the guitar, I'm probably going to go with a Hoffee. Go their site - watch the videos - those things are unbelievable.
The new Reunion Blues Continental Gig Bags are pretty awesome
So they advertise these things by shooting a video where they drop it off a 4 story building. While I'm not confident that would actually work on a guitar like mine. However, the combination of a really well padded-gig bag with a semi-rigid exoskeleton is a real breakthough in gig bags. Each and every facet of the gig bag is well thought out, with the hideable backpack straps being particularly amazing.