I think that sounds like a good plan!
One thing to note is that it might take a bit more than 4 weeks to get your residency card in Malta, particularly when you register as self-sufficient. So I’d recommend registering ASAP upon arrival.
Which makes me an ordinary resident, right?
There’s a difference between being a legal resident (meaning you have a right to remain in the country), vs being a tax resident. Registering as self sufficient will make you a legal resident of Malta, but it does not confer tax residency. “Ordinary resident” isn’t exhaustively defined in Maltese law, but it’s my understanding that it means you’re living and spending time there in the “regular course of your life”. If you spend more than 183 days there per year, then that requirement is definitely/automatically considered true. But by spending every winter in Malta, that could very well mean you’re “ordinarily resident” as well, it’s just not as black and white.
As long as you’re not spending more time in any other country than Malta (say you spend the rest of the year traveling)—or that if you do spend more time in another country, that country does not consider you a tax resident—then it is very unlikely that you’d run into any issues.
Note that you could still have limited tax liability to other countries. Say you spend two months (or a single day, for that matter) in Country X while doing freelance work from your laptop, then that country could ask you to pay tax on your income for those two months. In practice, the chance of most countries caring about you registering and paying tax there in such a situation is slim to none. Still it is a theoretical possibility, and could in many cases be required if you follow the letter of the law. You can read more about that in Streber’s The Permanent Traveler. PwC’s tax summaries can also be of help when doing quick research for requirements and laws of the various countries you spend significant time in.
Is renting an apartment for the entire year necessary?
In practice not really, as long as someone living on the address they have on file for you is willing to open or forward mail to you.
On a different page, I heard that it’s recommended to bring at least some of your income to Malta and pay tax on it. Is there a recommended amount?
There’s not really any “minimum” or specific recommended amount. It depends on among other things how much time you’re claiming to spend in Malta and how you are supporting yourself.
Are you living off investment income which would not be taxed in Malta even if you bring it in to the country, then why not bring in all of it? At the very least, I’d recommend bringing in enough to cover your rent and basic living costs like groceries for the time you are claiming to spend in the country.
Note that if you do spend e.g. 2-3 months per year in Malta and do work (say freelancing, consulting, writing, or any other type of work) even if it’s for a client outside of Malta, the income it generates is still considered Maltese source, and should be taxed in Malta.
Leave home country and fly into Malta
If you are currently resident where you are a citizen and grew up, then that country might have certain requirements in order to let you become a non-resident for tax purposes. So just make sure that’s not the case, or alternatively that you fulfill them all by doing what you outline above. PwC’s tax summary might have some useful information for your home country in this regard, but it might be better to do some additional Googling or checking with a local tax adviser to be sure.