Here's a quick attempt to answer your questions.
1. If you do nothing for the rest of the year, you will be Gold for 2016 and rollover 14 nights to start the year. You'll get the 15 credit card nights in Feb so that will essentially put you 29 nights toward retaining Gold or achieving Platinum in 2016.
2. To reach Platinum this year, you will need to find those 11 nights somehow. If you could move your January event into this year (or plan a different one before the end of 2015) and stay one additional night, you'll make it. There is no way to "buy" your way to the next status. If you had been Platinum this year and failed to renew you would get the chance to "buy back" your status for 40,000 points.
You'll have to decide whether you want to rollover the 14 nights or try to rack up 11 nights between now and Dec 31.