Dragon-Fire

[Raynor]

they did send him off after the Ring was made didn't they?

Sauron made the One Ring in the year 1600 of the Second Age, (which lasted for ~1841 years more); at about 1000 years into the Third Age, the Istari reach Middle-Earth (cf Tale of Years, ROtK).

Do you think they sent him off blind to defeat Sauron or do you reckon they gave him a bit of background information before?

I don't think they had much detailed information. The istari were Sauron's peers (in nature and strength - or at least before they were embodied) so they knew each other anyway; moreover, their sending was "a mere prudent plan of the angelic Valar" (only at about 2060 do the istari fear his return).