You just broke my brain. I need to dig into this. More clarification would be appreciated.
So the math goes like this (rounded to the nearest $5k):
Proposal:
$125k initial portfolio balance, including: $260k TSLA - $135k margin
Shorting 4x June 2023 750 calls which adds $100k cash, your portfolio becomes: $260k TSLA - $35k margin - $100k short calls = $125k still.
Withdrawing $100k for down payment on a house: $260k TSLA - $135k margin - $100k short calls = $25k
What you didn't account for was the $100k you get from selling the 750 calls wouldn't add to your portfolio balance immediately because their time value would still be $100k.
It'd be technically impossible for you to withdraw $100k cash even after you have sold the calls. You can't borrow $135k while your account only shows $25k, unless your last name is Hwang.
Now, if you buy 5x 400/750 spread, each costing $12k instead:
$125k initial portfolio balance, including: $65k cash + $60k in spreads
Withdrawing $100k, it becomes: -$35k margin + $60k in spreads = $25k balance
If you calculate your return by dividing the potential value in June 2023 with both legs ITM by the premium, you'll end up with $175k/$60k - 100% = 191.67%
If you calculate your return by dividing the final account balance by the initial portfolio balance, you'll end up with $(175k - 35k)/25k - 100% = 460%. Basically you put down $25k today for a chance to win $115k in 2 years. Now, not many brokers will allow you this much margin to spend on spreads. On shares, sure, but options are deemed much riskier. I think some will, though. What you'll likely end up doing is skipping the whole withdrawing $100k all together and just:
(1) Deposit $25k into your account with the highest option trading level your broker allows (I suggest a TD advanced account)
(2) See how many spreads your broker allows on margin
(3) Get ready to deposit more money to keep the position afloat.