Buying my first car, used. Few questions and need suggestions

Can I get a decent used car under $5000? Plan is to buy a used one, get used to driving and buy a new car in 2 to 3 years. Daily average 30-40km. I can spend a collective of $1000 extra for a 3rd party android auto/carplay unit, dashcam & backup cam. Is under 250000 kms fine? Currently I'm looking on Auto Trader app where it shows cars from various dealerships. Which dealerships to avoid? Should I get a mechanic with me to check the car? Plus any other tips please! Thank you so much.