Can you get by using speedlight canon 600's on umbrellas with an St-E3 or should I stop kidding myself and get a nice flash setup? I have 2 600's and the umbrellas/tripods. Was thinking of alien bees or white lightening.
You can probably get by
with just about anything. You'd get by with a desk lamp if you had to. So do you merely want to get by
or do work that is relevant and creatively aligned with your needs & vision.
So as privatebydesign suggests, without a clearer explanation of your intentions, it's a tough question to answer. Nevertheless, as you're talking about umbrellas and ST-E3's, Alien Bees or Einsteins will free you up incredibly compared to your current setup. The 600's are throttled back with low output, slow recycle times, no modelling lamp and in the absence of expensive high capacity external batteries, an over reliance on a huge supply of AA cells.
No one setup will do everything for you. You can't beat your 600's for events and other obvious jobs that by their nature require flash on camera or very compact lightweight solutions, but the Alien Bees or Einsteins will come to the fore when you're doing studio style work, whether in your studio or certain location projects.