What should I do with this keg?

I got a 15 gal keg for 40$ today! Making it my first piece of brewing equipment!

But... Now I dont know what to do with it? Should I turn it into a HLT or a Boil kettle?

I was thinking about getting these

http://morebeer.com/view_product/15631/102307/B3-
200_10_Gallon_All_Grain_System




And does anyone know if this comes with 2 10 gal coolers?

http://morebeer.com/view_product/20863/102307/B3-250_10_Gallon_All_Grain_System_With_Thermometers


Tell me what you think my next move should be!

Make it a kettle. But, you can make the MLT yourself for a fraction of the cost. The link below is for Batch sparging, but there are plenty of threads about fly sparging and the concept and materials aren't that much different.

https://www.homebrewtalk.com/f51/cheap-easy-10-gallon-rubbermaid-mlt-conversion-23008/

If you don't have a kettle to boil 10-12 gallon's I would make it a BK.
As for the HLT/MT... I would look into making your own. I used coolers for some years and making my own stuff cost me a fraction of what you will pay in that link. However, it's all in what your time and abilities are worth. I have purchased many items I could have made myself but just didn't have the time to get around to it. You know what I mean, your time is worth something.
And in the long run if you will be going to all keggles, just start looking for one or two more for your HLT and MT.
Good luck.