Very important. Especially SEO will take one important part in den digital marketing business. This is no wonder. You get a lot of clicks for free 24 hours per week. But you have to invest. Small business hold themselves a little bit back from investing money but there are interesting approaches and concepts like the go-digital fund programms what I have seen here.

No ,they don't.

It depends on the CMS and the topic. Is it a shop or a small blog.

I would set all parameter URLs to index and set the canonicals.

Scale down big images, eliminate CSS & Javascript where it is possible, switch your server.