It's best to have as much content as possible and fresh is always good. That would most likely be in form of a blog where you post maybe 3-5 times a week. A blog helps you connect with your market.
Images, video and audio is all great. I need to work on ALL three of those LOL
SEO is a complicated thing, well for some like me who took over a year to finally get it. I'm still a bit gray on the back linking aspect of things. BUT on site SEO is making sure you are using keyword phrases that fit into your content. Use it as a title, in the content and as the link. Does this make sense?
I can try to help you if you give me an idea as to what you're working on.
You're right, link pages are really a thing of the past. Exchanging links really doesn't do much these days.
One way links are good, yes! Maybe you could offer to write an article for someone's site or be a guest blogger or something like that.
I'll be happy to help answer your questions as much as I can.