Buckster, first let me congratulate you on taking a step to improve your outward appearance and, I believe, the inner man as well. It's hard to learn new tricks.
I would say the first thing to do is try to learn what fits your body and looks good. As a general rule, most men wear their trousers too long, their shirts too big and jackets simply don't fit. It makes them look fatter and shorter than they are. The Flusser books are a great way to start to learn this. Sometimes they veer into some stuff you don't need to know about (how to pick white tie vs. black tie), but there's some good stuff in there.
The other aspect that's not easy is remembering to dress your age. It's easy to say "I need to update" and end up buying clothes a 19 year old wears. "Queer Eye for the Straight Guy" did this in spades. But it sounds like your model is good -- Clooney dresses like an adult in the Oceans films.
In addition, tend towards the basic colors to start: white, tan, gray and navy. But learn how to mix and match.
Once you have the fit down and look in your head, remember you can dress well spending $10 or $10,000. The trade off generally comes from how much effort you want to put in to clothes. You literally can dress very well buying from ebay, the Salvation Army and discount stores; but you have to dig. Or you can walk into a luxury department store or boutique and get fitted out. But having the above knowledge will be key.
If you're on a learning curve, I'd stay away from catalogs and websites for a while. You need to get a sense of how things are supposed to fit and what looks good and that's hard from a web photo. Instead, go to stores that you trust. I would generally recommend going to an old world store in your town or city where some old guy knows how to fit a jacket, as opposed to a 21-year old who doesn't. But that's just me.
For brands, I would say that Brooks is a decent brand at a semi-high price point. You're rarely getting a real steal, but rarely are getting something terrible. Polo is trickier, and you're paying for advertising. Department store brands can be very good deals as well.
Also, don't be afraid to post pictures of yourself and ask for critiques. It's tough, but it's helpful. There's a well known old-time poster on here who started doing that when he first joined and his clothes, well, sort of sucked. Now he sometimes posts his bespoke clothing and it look vastly better. He sought criticism to improve and improve he did.