This advice is spot on. I would add one thing: make sure you don't surprise your manager. Talk to her. You and she should be on the same page about your project's progress.

It's her responsibility to help the rest of your business do the best they can with reality. If sales of your existing product have dried up because prospects are waiting for the modernized one, that's a big problem (been there). But it's a problem belonging to product and sales management, not you. Unless you are a founder.

Renovating software is hard, much harder than greenfield software. All the best to you.