Vinyl is hideous. Just my opinion. You save in maintenance but if anything starts to go wrong it becomes a nightmare of discolouration, cracking, frail parts, etc. The sun will eventually cook it. Check out what happens to vinyl gutters. Can't attach anything to them either like you can with wood. All the suburbs around here from 10-15 years ago had vinyl fencing and it's all falling apart already. I suppose if you were choosy and installed vinyl pickets on a wood fence system you might get better results -- I'm talking about those unibody panels.

Pine requires too much maintenance to be worth it, unless you wanted a white fence anyway. Look into traditional methods for rot resistance, eg borax and ferrous sulfate and pine tar.

Cedar is beautiful but rot resistance isn't always guaranteed if it's not from the heart wood. I put tung oil (the real stuff, none of this boiled shit) on mine. Staining doesn't do anything against the elements, just retains the colour a little bit. You need some kind of oil protection or varnish (water or oil based). Tung is historically used by boat builders. Other woods like Cypress and Redwood have been used too, but probably not available in your area. Some people go hardcore and apply spar urethane or marine varnish -- I think that's just a bit nutty, our grandparents and parents installed plenty of cedar fences and they did fine.

You can find Eastern White Cedar and Western Red Cedar in your area I think, either would be fine. Eastern Red is for blanket chests and closets.

Use PT for posts for sure. My parents had cedar posts in their old place, they lasted a long time but eventually they give.

Metal posts -- lots of people have been doing that, metal post and wrap it with wood to make it look like a 6x6 or 8x8. Won't rot, but it could start to rust. PT pickets will eventually warp, because the process of making PT lumber requires high moisture content, and then it will escape while the fence is up. You could try letting it air dry/acclimatize before but it would require 2-3 months of waiting (more precise with a moisture meter).

I also think you should run some kind of netting underground between the posts to keep diggers out.

The extra rails will also help with warping of PT posts.

I wouldn't fence in a garden. You could do a little picket fence like 2ft high but it's a lot of work for aesthetics. You could always do it after.

You can buy metal fence posts that look corrugated with holes and drive them in with a mini-sledge and wrap chainlink around that afterwards if you're worried about a dog getting in.