How many SEO articles is a good amount? To start and per month?

Interesting, how come?

Lol, your stuck on associating SEO with articles.

In case you haven't figured it out yet, 99.99% of anyone advertising SEO articles will sell you 3rd world junk.

Dude... Do you mean quality content that you can rank or rubbish BS content that will get you penalized?

If you want real content try these:

constant-content.com
textbroker.com
writeraccess.com
freelancer.com
upwork.com

Expect to pay .05-.15 cents a word for quality content.
Or write it yourself.

You might be able to find a sweet spot where you are paying less then .05, but then have to edit the content and make it "publishable." If you choose to go this route, I highly suggest grammar.ly (the premium version.) I still suggest you pay 2-3 cents a word or it will be complete garbage. No respectable writer is going to write for less then that. At least at 2 cents, a freelancer can bust out an article in 30-40 minutes and make a decent amount, but you really need to feed them 2-4 examples and keep your requirements to a bare minimum. This only really works for basic articles. If you expect somebody to write a technical 500 word article for 10$ you're going to get garbage as well. It needs to be topics average people know about and won't have to do much research other then reading your examples/resources.

#1 This doesn't really matter, when I was doing static sites I would do 10-20 pages mainly because it was less work that way, since I have to mass edit every page when I updated the site. Having all the category pages setup meant that I only needed to edit a handful of pages. I don't do static sites anymore since updating them to mobile responsive sites was a pain, so I just converted them to WP sites. If it's a WP site, just start with 1 page like normal bloggers do.

#2 No. Maybe if you publish 100+ a day or something insane. Good luck even putting 100 articles into WP in a day. If the content is pre-written and edited, I doubt I could do more then 4-5 an hour. There's still a bunch of jacking around in WP to set the category, upload images, featured image, meta descriptions, possibly add in links, bold, italics, oh and fix the formatting of the new lines (FML...)

#3 1 a day seems great to me. Sometimes I just do 1 a week, but I run a bunch of sites, so 1 a week per site. If you want the site to be big, 3-10 a day. The rate you publish content matters far less then the quality and value of it. It's also highly recommended that you mention that you made a new post on your ideally developed social media properties with real followers and people who want to read your content. I don't suggest spamming the crap out of them with 10 updates a day. Some people post once or twice a month and their sites make 20k/month. Some sites post 30 times a day, but it takes a team of people to accomplish that.