As far as I can tell everybody who goes to the track is a "pretty good handicapper" but doesn't know how to maximize their bets.
And believe me I'm certainly not one who has any right to be giving advice on this subject.
But. But because you asked, and to open up on the discussion on this subject I'm just going to throw out a few notions.
Now it seems to me that the bet that offers the best opportunity to capitlize on the confluence of knowledge and bankroll is the pick four. That the pick four offers the best opportunity to cover yourself for the least amount of money and still occasionally make a score.
My strategy is this: Play three horses in each race for $1.00. Cost $81.00. Then play two horses in each race for $1.00. Cost $16.00. And since you're up to $97.00 you might as well play one horse in each race for $3.00 (on $1.00 tickets.)
So now you've invested a $100 but you're in a position to hit the pick four for $5.00.
The key to this strategy being that you indeed must be a pretty good handicapper. But the results should prove that out. For if, with this much coverage, you're not hitting at least one out of five bets for at least a dollar, you really aren't as good a handicapper as you think you are.
And my take on another one of your questions, namely how to fill out exotics is this: Whenever possible use fresh horses and/or horses cutting back in distance for third and fourth.
But again, I offer these notions not dogmatically but just to open up the discussion.