5,Poznan is cold?
In the space of 6 weeks, it went from -15c here to +10. The swing this year has gone from nearly -20c to +30c. That should tell you all you need to know ;)
1,i can manage my self in Poznan becoz i have only know english to speak ,write,,read,
Shouldn't be too difficult as long as you have someone to help you out. The biggest problem you'll have is with the Urząd Miasta with the zameldowanie nonsense.
2,i can get hotel ,bar ,cafe, any jobs?
It'll be tough with no language skills. I'd advise trying the larger hotels and see if anything comes up, but I'd suggest learning the language as soon as possible. English teaching is likely to be a no-no for you, unfortunately.
3,i can get little good amount of salary ?
4,how much i can get pay?
10zl an hour might be doable. But I would prepare yourself for the worst - 5zl in the hand might be the most you can hope for. It depends on what you find - I'd actually suggest hunting down the Easyjet call centre and seeing if they've any use for you there.
All I can really suggest is perhaps going to Dragon and running into the expats there - someone might very well help you out or have some connections there.