The resort airline center is located at luggage services. If facing the main building from the outside, this would be on the far right corner of the building at POP.
Your magic express bus will leave POP for the airport about 3 hours before your flight time. Check at POP desk for exact time. For your 4:10pm flight this means about 1:10pm so be back at POP before this.
You can check your bags in at resort airline center. This is the same as if you were at the airport yourself to check luggage.
For southwest, make sure to check in 24 hours before your flight unless you paid the $10 extra per person for automatic early check in. You can do this online or go to guest services at any Disney resort or park and they will do it for you. I use my cell phone to log into Southwests website to check in 24 hours prior. This gives you the better seat selection as you'll board before most others.