Before you buy anything do Intro To Tech. Part of the point of the training is to help with knowing what you need to buy.
ITT is a valid option, but depending on the OP's experience level, it's not necessarily the best class to take. If you, the OP, are still a n00b and just getting interested in Tec diving, then ITT could be fantastic for you. On the other hand, if you've got excellent buoyancy and experience blowing bags, then your AN/DP instructor could incorporate the how-to-dive-a-twinset into the course. I, for example, learned to dive doubles during my Tec40 class.
You should prioritise the drysuit. That has to fit and is hard to borrow or rent.
Don’t buy a secondhand suit. You may be buying someone else’s problems. Don’t go mad on options and cost unless you have money to burn. You don’t want complications like dry gloves yet.
I halfway agree. Going nuts on options is a sucker's game. My first drysuit was an entry-level "Dolphin" suit, by OS Systems out of Scappoose, OR. It cost me $800, including a fleece jumpsuit, and I used it for about ten years.
That being said, a used drysuit isn't necessarily a bad option. If standard sizes fit you well, a used drysuit is a massive moneysaver, much akin to buying a used car versus a new car. Plus, if you hate that particular drysuit, you can likely unload it at the same price you paid and try another variety.
Dry gloves, though, could be a near-necessity for you in Oregon. Don't make them a deal-breaker item, but if your fingers get numb on your regular, recreational dives, you'll definitely want dry gloves on deco dives.
Then do Intro To Tech. The idea here is to learn about kit, configs and so forth. Trying to buy the kit for the course that teaches you about kit is backwards and may lead to questions like “Why did you feel the need to have two bladders in your wing? Look round here at these 50 other divers not on courses but diving twinsets and ccr - do they have that?” while your buddies careful scrutinise their fins to avoid the painful look on your face.
I've taken classes from two tec instructors, and they both demanded double bladders.
*shrug* Choose what suits your instructors and yourself the best.
Aqualung is kind of the same as Apeks, it is the parent company, but I would choose Apeks and mix brands to start with. Where you are that might not be best as Apeks is relatively expensive there.
Were I in Europeland, I'd prolly get Apeks, but not here in the States. It's pricey. Get something that's easily serviced in your area.
If money is an issue (and it should be because you’ll be needing a bigger house) then this sort of kit [harness, backplate, wing] can be bought second hand.
YAAAAAAAASSSSSSSSSSS.