There are a few ways to play this - and it may depend to some extent on what you spend the $200K per year on.

There are some point earning cards from Citibank(platinum amex) that, for example give a 3% rebate (3 Thank you points) per $ spent on any purchase - there is an annual limit of 150,000 TY points per year (so $50,000 x 3pts/$). This limit is PER CARD, not per Thank you point account. So no reason why you cant get one card, spend $50K on it, then say 3-4 months later, apply for a 2nd card, spend another $50K on it, and repeat again.

Also consider the Starwood AMEX card - this gets you 1 point per $ - but one of the options on this card is you can convert points to airline miles (just confirm UA is part of the program). BUT YOU GET A BONUS: for every 20000 points you transfer for miles, you get an added 5000 miles.

So 200,000 points = 250,000 UA miles. Again check for annual limits.

BTW - you can get a personal Starwood and a business starwood - each with a 10,000 point bonus when u get a new card. So if there is an annual limit it would be PER CARD, so effectively doubling your annual limit.

You can also get a United Credit Card (again get a personal and a business card) - assuming you have not applied for these in the past, there are links available to earn 25,000 UA miles per card.

You are right that this is CONFUSING and some people explore the ins and outs of maximizing credit card bonuses and rebates.

Small example - let us say that $10000 of your $200000 is on gas - now some cards pay a 5% rebate (cash or Thank you points) for GAS purchases.
So would $500 cash rebate say be better to you than 10,000 UA miles (which in this example means the UA miles cost 5 cents per mile - which is alot).

I hope this helps a little - Happy Holidays