Agapi - the amount of pretreatment you need depends on what you want to do with the cells. Are you simply measuring their presence or purity or sorting for culture or other analysis. Also, are you using human or mouse as your starting material? The ADSC panels I'm familiar with are more extensive than just CD90/105, in large part due to the broad heterogeneity of the non-adipocyte stromal cell population and the presence of some amount of contaminating blood.
Could you be a bit more specific about what material you're starting with and what you are doing with the ADSCs?