Painter for 20yrs. Writer for 6. Can I combine both in an author's site

Sure. Why not? As long as the pages are clearly identified in the menu.

Why do you need a separate website from your blog? If you have a WordPress site, you can create static pages.

Personally, I think a website/blog is better. The blog keeps changing as you add new posts, so there's a reason for people to come back. If they keep coming back, they'll know when you have new releases.

I don't think there's a problem with having your paintings up, but it's up to you what the focus of your blog is. If you have a section on paintings, but most of your posts are about writing, I don't think people will be confused. Writers who are also visual artists aren't a super-uncommon thing.

I'm a painter, too, although most of my current work is story-related. I'd rather paint my own kelpies, unicorns, dragons, etc. than use someone else's work. I think the best way to tie the two together is to use your artwork with your posts, if that's possible for you. We all need graphics for our posts anyway. Maybe you can write stories to go with your art.

If you're going with tabs across the top, you can always put your art in its own section.

I don't see any problem with including writing and painting on a single website. Just keep unique pages for both. Good luck.