1. SEO Tool
a. Since you're doing it in-house, even if you end up getting data from multiple sources, having one tool to standardise your search volume metrics will be helpful down the line.(everything is inaccurate but at least you get comparative data)
b. Compare some of the common tools for keyword data in your industry. Eg: For one company, Moz was better, for another SEMRush was better.
2. Competitor analysis:
a. For at least the US, I've seen SpyFu work the best.
b. Your primary tool will also have competitive data, so use that as well.
3. Grammar/editor
a. No comments here since I haven't tested too many tools.
b. You can also consider using tools like Surfer for SEO alignment or
Jenni.ai for AI based research.
4. Project management:
a. I've seen a lot of companies complaint that having a different project/workflow management tool is really causing a lot of issues in cross team collaboration. I would try using whatever you have before trying something new.
b. A simple Google sheet with good processes apart from whatever you use has worked for all the companies I've seen.
c. Consider non-SEO distribution channels and thus stakeholders when creating this channel.
Note: Don't try to make every piece of content needs to rank organically. There are a lot of other uses for content. Identity which content pieces are for organic channel ONLY, vs which are for other channels only vs which are for a mix of two. Eventually this is what defines what kind of ROI you may get.
Note 2: Usually highest SQL generating content are not blogs/ebooks/guides. Make sure you have some flexibility to create other pages like software page duplicates and micro tools when you find a great opportunity in your keyword research process.