Say I have in my portfolio:
100 TSLA shares
1 TSLA LEAP (eg Jan 2023, $1000 strike price)
$0 (zero cash)
I then sell a covered call against my TSLA shares. I can sell exactly one covered call. I sell a weekly for example.
Lycanthrope's explanation seems to imply that I can sell a second covered call, against that LEAP.
Not sure about the interpretation of the explanation but in this scenario, at least for typical brokers, you cannot sell a call against the leap. You have no collateral (cash or margin) for that sold call. The shares are already being used as collateral for the first covered call. The LEAP itself requires margin equal to its value (so its basically self covering...though maybe that's not the best way to describe it...?), and the zero cash is a goose egg.
I understand that the CC I sell against the LEAP must have a strike equal to or higher than the LEAP strike price.
Unique broker rules aside, this is not a requirement. If you sell a call above the +C strike you won't need to earmark any more margin. If you sell a call below the +C strike you will require standard credit spread margin, which typically will be [$ difference in strike * 100 shares * number of spreads].
I don't understand where you state that the expiry of the CC must be prior to the LEAP.
The expiry of the sold leg of a calendar spread must come before the long leg in order to fall into spread margin requirements. If a -C expiry is after the +C expiry in a calendar spread that means--in the eyes of your broker--at some point in the future the -C will be naked, because at some point in the future the +C is going to expire. With a typical broker and sufficient options trading level and sufficient margin to satisfy naked -C margin requirements you could absolutely create that position; the point is that regardless how long you intend to hold the position the broker will always classify the -C as naked.
***Its possible some brokers internally layer trading rules on their customers to minimize the amount of trouble those customers can get into.
In my mind it should be an expiration AFTER the LEAP expiry. That way with the passage of time the LEAP will convert to shares and then those 100 shares are covering the covered call.
There's really no value in coupling the two contracts. The -C is going to be naked and the +C is effectively just going to be a standalone call, you might as well just treat them as such. (Its also a terrible idea to sell a super long dated contract, but that's another conversation)