Is a OnePlus phone for me? Looking for feedback/advice

I'm currently running a Moto G3, with 1GB RAM and 8GB storage, which I've had for a year and a half. It's served me well, but it's showing its age rather badly. I'm looking at options for a replacement, and want your input about the current OnePlus phones.

I'm in Canada, and my budget would max out around $400-$450. I'll give a laundry list of things that are important to me in a phone, and I'd appreciate your input:

• General reliability - I know that every manufacturer makes a lemon once in a while, but I want a phone that I can rely on not to act up or do crazy stuff without my telling it to.

• Camera - This is important, not least because my phone is my main camera. In good light, results on the Moto G3 are quite acceptable. Indoors, in dim light, or in glare, I'd like to upgrade to something that can do better. I would also like a camera that is faster, both to launch as well as to take the picture.

• Performance - Something with more RAM would probably be better. I don't play intensive games, but I have a few apps that have somewhat heavy libraries. I don't like having my phone freeze on me when I open an app.

• Screen - Moto G3 is a good size for me; I can read on the internet and watch YouTube. I don't want a phone so big that it's hard to get into my front hip pocket, though.

• Software - I don't appreciate aftermarket skins such as Samsung's TouchWhiz. Leave it stock, or at least close! Moto G3 is good in this regard. I've heard that Oxygen OS is close to stock. BTW, I really like stock Android's DND ability; how does OOS functionality compare?

• Battery life - Good enough currently. Usually only runs out after heavy navigating.

• Updates - I don't like having my phone over a year (or a month, for that matter) out of date on security patches. When I get a new phone, I would prefer to have some assurance that it will get reliable security updates. It seems that OnePlus updates their phones promptly, but over a rather short life cycle; is that accurate?

• Lifespan - I'd like a phone that doesn't feel like it's on its last legs within 1.5-2 years.

I've considered the OnePlus 3/3T, but buying it new is a bit on the expensive side. Additionally, reading comments I've heard some negativity around OnePlus' customer support; however, I'm also aware that people with negative experiences are much more likely to get loud about it than people with positive experiences.

So, I'm considering shopping eBay for a used OnePlus 3/3T. Do you guys think that would meet my needs, or should I maybe wait for the details and price of the OnePlus 5?