I am studying a protein involved in DNA damage pathway. For my experiments, I wish to treat HEK293 cells with genotoxic agents: bleomycin and florouracil and UV. 

My protein of interest is halotagged (for pulldown) after which I wish to use gel filtration to get to separate any protein complexes that may be formed and how they vary in each pull down.

However, I do not know how many cells I should start with to get a good separation on the gel filtration column. any ideas.