My main place of work will be in Glinojeck,gm.Kondrajec Panski,Poland
At the sugar plant?
Generally the people in Poland aren't especially racist and are generally polite, but be aware that Glinojeck is quite a small town with small town attitudes. Having said that, British Sugar employs a few foreign people, so you won't be alone. If you are black, people will notice you and stare, but that doesn't mean they're being rude - it just means they don't see many black people.
You didn't say if the 900 euros was net or gross? Assuming it's gross, that's ok for Glinojeck since accommodation is provided, but you'll have to live quite frugally (easy in Glinojeck) to be able to save a good amount. If it's net, it's not at all bad for somewhere like that. Visits to Warsaw are easy from there too.
If you are living in or near Glinojeck, you may be able to give private English lessons, since there is a shortage of native speaker teachers round there (and the sugar plant was having problems finding any).
It doesn't seem a bad offer. If I may ask, what kind of work do you do?