I am going to use it for a coil, i am using PWM and some transistors now.
I just burned my IRF520 transistor smiley-razz so would like some alternatives.
You made two mistakes that caused the failure described in your post.
1 The mosfet was under-rated
2 The flywheel diode was in the wrong place.
You have already been given suitable recommenations for a mosfet that can handle your load but unless you have the flywheel diode in place (1N4007) across the load , not like your schematic, you will continue to blow anything you use.
Mosfets in parallel is a standard practice in many applications. Parallel transistors is the same concept but mosfets are more efficient and therefore dissipate less heat.