I have a huge break on codeforces for last few month(s). I want to back to codeforces.i am now ~800 rated after 13 contest :). I do cf as a preparation for IOI. can you please help me with answer of some questions?

1 When should i start OI psolving. I had known that OI problems are usually very hard.So is there should a boundary of rating in cf to star? [i am predicting there should be]

2 For that rating what should i do?

3 is there any OI problem list sorted with difficulty?

4 is it possible to crack in 1 year & get a Bronze(?) medal

Or any advice for me to prepare me for IOI (if you want)