They never had a manager and worked in a silo'ed way, with developers getting assigned to different projects as needed.
The CTO/CEO want to improve the teams quality, have better processes, etc. This team performs user-visible tasks.
What do you usually expect from a new manager? If you were said manager, what would you do?
Understand that all change is going to have a personal impact of each one of them. Knowing the above will help you know which people will be happy/angry over change, and you can work with them to help them understand the context of why changes are needed, and what the future holds.
And don't make change for its own sake. If you cannot justify how changes are better for the team, the company, the product... then you should not be making changes.
* Get to know the people in the team, learn the overall vibe of the group, and how happy everyone is.
* Get the know the people above the team, their motivations for hiring you, and the tangible outcome of your hiring. You say "quality", but what does that mean? Is quality currently low? Do they feel that they could be doing more in certain areas?
From there, I would typically work to integrate myself into the team before introducing any changes. If the average person has been there for 2-3 years they've got a lot of business knowledge that I won't have. In my experience, most teams have a strong opinion of what they want to do to improve processes, but there is a business reason as to why they've not implemented those improvements.
The last time I led a team, I wanted total transparency, so we came up with an internal list of improvements and we focused on incremental and manual improvements to processes. Most of the time I wasn't even the person making the changes - I was picking up the slack so someone else could do the work, or do something they've wanted to do for months. Our processes improved over time, and as a result delivery improved dramatically. This introduced its own problems, but in the grand scheme of things the problems were nothing compared to before.
All I expect from a manager is honesty and consistency in feedback, so when I've been in those shoes I've tried to be as honest as possible, and to be as transparent as possible when my message isn't consistent with what I've said before.
You can only do this once, and you can only do this at the start of your tenure. It's in your interests to do it, lest you find in six months that your legs were shot out from under you by the previous administration and you didn't even know it.
Leave your ideas at the door and assess what is good for the team. For example you love Gaant charts and were super successful with them at your last company. Don’t introduce them here unless appropriate and probably not at the start. Unless perhaps everyone else is asking for them and it makes sense. What I am getting at as it shouldn’t seem like you are bringing your ideas and commanding, but you are listening and leading.
You also need to do the same exercise upwards too! What does the boss think the problems are and how will you address them.
Find out what the tension is between the works and the management. There is always something!
Once you know that your job gets easier, you now need to figure out how to get the team from the place they were to the place that the executives want them to be, remove blockers etc.
Don’t try so much to quickly enact processes as much as listen to what’s working and not working currently.