SEO - transferring domain

Hi,

Got a website that ranks many terms in its niche in the top 10 on Google ... my client wants to move to a new domain name - we have built his new website with tons of new content and much better optimisation on page. Should we be able to just 301 redirect and match the redirected pages to their new replacements and maintain rankings? Anyone with experience in this and help/advice/things to watch out for would be appreciated.

I recently did it. I was on the first page for most results. Firstly go to Google Search Console and let them know you're redirecting it. Eventually, the domain / url will update (takes around 2 weeks). BUT I've noticed an overall drop in ranking. My new site doesn't even appear in the top 10 pages for certain keywords even though the old site appeared on page 1.
I'd suggest redirect in Search Console first then your domain provider, set domain to Permanently moved under the forward settings. You'll need to update your Google analytics code too. Best of luck

This is an interesting problem to have, and from what I can see, a very informative answer.

There will be a rank drop for sure specially it's a brand new domain. I did something same like year ago and I'm still recovering. It gonna be even harder if you keywords are competitive.

There will be many variables that you will need to take care of - for instance not all 301 scripts/code is similar, as there are variations that may not properly redirect to the sub-page, etc, and hence either a broken link/404, which is a red flag in the process.
So you will need to make sure that the redirection can mirror exactly the sub-URLs, otherwise, it will open up a whole new can of worms/problems.
Based on my personal experience, you will experience a ranking drop as the initial domain is now no longer available. The new domain which is entirely new, will not have any metrics, and would depend on that 301 for the link juice.
301 does not pass 100% of the link juice. Some put the figure at 70%, some at 90%, but never 100%, thus due to this fact, the new domain will not mirror a 100% of the old domain on the SERP ranking.

It's really difficult to come up with a long-term solution for issues like this, especially because you are dealing with a new domain. There will really be occasional drops because of Google dance.

There's an in-depth guide about this that I believe would help you.