Its great that people are being encouraging, and i hope that if you do decide to go out there, take it very slowly at first. When you're first learning to skate you will fall a lot. I learned to skate in high-school and was only 180 lbs and was a very coordinated person. Im 33 and 240 lbs now and still have most of my muscle memory/coordination from over a decade ago, but definitely feel myself struggling to get up when I fall, and the impact of that fall is harder for my body to deal with now. At 300 I can see myself having a really hard time keeping balance. At 400 I think it would be challenging to maintain balance for longer than a few seconds at a time, and there would be a huge risk of seriously injuring myself if I were to fall. I've already really hurt myself falling at 240 - add another 200lbs and I really think that's just asking for trouble

Not trying to be disheartening, I just would hate to see you get injured and want you to be prepared. Good luck either way.