It's definitely a DIY job. We've just worked through 12 and also had 3 replaced by professionals. Having seen how they did it I wish we had just done it all ourselves, it felt like the worst 5k we've spent renovating.
I hadn't realised how easy it would be, but once you have the beads out you can bring the windows inside and can scrape them and sand them back. The external work is also straightforward if you have a ladder to get to them, or you might be able to paint them inside then put them together after.