You can apply chase ink credit card for another 50000 miles

Chase ink card points can be transfered to united mileage account as well. So another 50000 united miles from chase ink card.
So you can have 40000 miles from Sapphire, 30000 from united Mileage credit card and another 50000 from chase ink.

Totally, you can earn 120000 united miles and enough for two round trip tickets to Europe.

However, applying too many credit card can hurt your credit score in a short term. Also, all three cards are from Chase. Not sure if you can get all three cards approved in such a short timeframe. So evaluate your own credit situation to see if your credit score is high enough to take a hit.

For meeting minimum spending requirement, take a look at this:
http://millionmilesecrets.com/2011/07/20/40-powerful-ways-to-complete-your-credit-card-minimum-spending-requirements/