new to f250 needing help

[bb250]

well i bought a 2008 ford f250 lariat. its a 2wd 6.4v8 supercharged. i love the truck and i cant wait to start doing some work to it. i bought it not knowing anything about the radiator leak, gasket oil leak... so i opened the hood yesterday and realized the coolant was low, so i was like ill go get some tomorrow. so today i got up and went and got it and fill it up to the max line. when i got home from autozone i went under the truck just to check it out (keep in mind im not a mechanic, i have no clue when it comes down to mechanical work) and i realized that there was kinda of old oil (dryish) under the motor infront of where the plug is for the oil change. after seeing that i got online and found this forum and other ones in reference of the same subject and people talking about all their problems with their truck. people that have gone thru like 5 radiators, new motors, etc. how do i know if there is an oil leak? or if it was fixed by the previous owner? i took a picture of what it looked like with all the oil, but i cleaned it afterwords too see if there is a leak here in the next couple of days...
what about the radiator? what do i look for to find if im having any problems with it? i put a mark on my coolant tank to see how much coolant fluid i loose over the next few days but i am a bit worry about all these problems, i mean i can afford the truck diesel but i cant afford to keep having to pay to fix it. I am only 23yrs old and i figured a 2008 f250 w 40k miles would have no problems. I live in north houston, tx. i did not buy the truck from a ford dealership which shouldnt really matter when it comes down to warranty work, recalls, malfunctioning, etc. how much does warranty cover? is ford reliable for these problems?