If I were buying today, I would be getting a LG C1 display or a Sony A90J if I just wanted the best looking display. If coming from a good CRT, then the OLED should look very good to you.
The biggest negative is that they aren't super bright. They are definitely CRT bright, but not as bright as the better LCD panels get. The Samsung QN90A or B series is a great way to go in a brighter room and if you want that brightness from a display and don't mind a hit to black level performance. This is the tradeoff right now.
Later this year, Samsung will be releasing a QD-OLED display which may add additional brightness to OLED while preserving great black levels... or so they say. Reviews aren't in yet and final analysis and recommendation can't be made yet. Oh, and you can't buy them yet either.
For audio, I might hold off a bit. The modern TVs have an optical audio output that allows audio from the currently playing 4K HDMI source to be fed into an existing AV receiver. So, you keep your existing receiver and surround sound setup and get the same quality audio you've enjoyed for years without making a single change to the system. If at a later point you want some added audio quality, then the speakers will remain the top place to begin with those changes. Plenty of discussion as to why that is, but it remains up to you if you want to make such a change.
