My first 5k on a treadmill. Goal is Marathon by end of May and lose more weight for better experience. Is it doable?

Current body weight: 213 pounds/ 96.5 kg Height: 5 ft 9 / 174 cm

Is Marathon a doable goal with my body if I keep training for next 3 months or I do not have enough time as I am a beginner?

Is treadmill training better or worse than outdoor actual run? thanks!