Reddit mentions of Sea Kayak: A Manual for Intermediate and Advanced Sea Kayakers

Books:
Sea Kayaking Illustrated: A Visual Guide to Better Paddling

Sea Kayak: A Manual for Intermediate and Advanced Sea Kayakers

Sea Kayak Rescue: The Definitive Guide To Modern Reentry And Recovery Techniques

Fundamentals of Kayak Navigation

Other tips:

a) Join a club if there is one near you.
or: Join groups with the same interest near you
Generally the quickest way to learn. Ask in forums as well.

b) You already mentioned courses. Def. do them. This is the best way to improve your technique.

c) Practise. Practise. Just paddle around, sometimes test and extend your limits in safe conditions (example: Go out in windy to stormy weather with waves [<7bft, on really big lakes <6bft] with onshore wind on a bigger lake you know well. Keep near the shore, learn how to paddle in waves. Paddle parallel to waves. Just get experience. If you fall in, worst case the wind will blow you onto the shore soon(ish). Know your equipment, always wear a PFD, have apaddlefloat, pump, reserve paddle & paddle leash, comms device and ideally a buddy. Train rescue & reentry first. Tell people where you are and when to expect you back)

d) Read a few blogs from people who did long runs on rivers and oceans. Even if they've used an open canoe, you can still learn a lot (equipment, conditions, duration and so on)

e) Maybe some youtube videos, but thats - in my experience - a bad source for kayaking. Lots of people who don't know what they are doing but think they are professionals.


For the multi-month solo trip: Your space is very limited in a kayak. It will be hard to get enough food for longer trips. For long tours a canoe is way better, although not really seaworthy. Don't go alone.

As you have whitewater kayaking experience, your biggest obstacle is learning more about the ocean and getting experience paddling on it in safer areas than the Inside Passage.

As you live in the Rockies, that would probably consist of some more trips to the PNW, for several days at a time. I'd buy a 17" sea kayak. If you can find something on Craigslist, great, but there's a lot of overpriced junk on there too. Then again, if you're in no rush, you can wait for something good to come along.

Here's a great guide on buying a kayak

The best how-to book on paddling the Passage is Alone in the Passage. It tells you everything you need to take, where to camp, where to send food packages ahead of time, etc. It's great.

The best book on ocean kayaking I've found is Sea Kayak. It covers a tremendous amount of material in a concise, clear manner.

One more book I'd recommend is Sea Kayak Navigation.

The three books together will give you a lot of what you need to know. They're worth reading and re-reading during the winter months while you plan your summer trips.