Personally, I do a yeast starter with every single beer I brew. (I am assuming you are using liquid yeast if you are talking about doing starters) I don’t think you run the risk of “overpitching” by making a 1 quart or 1 liter starter. Generally, the only way you are going to overpitch yeast is if you are dumping on an entire yeast cake or something like that.
However - make sure your sanitation is every bit as good for your yeast starter as it is for your beer.
As far as secondary - I don’t use secondary, and I think it is one of the single best things I have ever done with my beer. I go with a 3 week primary for ordinary beers, then into the bottling bucket or into a keg. I have seen no convincing evidence that a secondary ferment produces clear or clean beer. Beer clears because it sits still and gets cold - that drops the yeast out. You don’t need secondary to do that. My beers are very, very clear without secondary. I think a 3 week primary allows for a more complete ferment, it allows the yeast to take up some of the undesirable flavors that may be produced early in ferment, and it reduces one step where infection could be introduced.
I do agree with other post though - if your beer was undrinkable, there is a problem somewhere and it is not yeast starters or secondary fermentation. Look at every step after the boil is off - something is wrong there and it is likely a sanitation issue.
How do you cool wort?
How do you transfer wort?
Do you top off with water? Is it sterile?
Sanitation of fermenter.
Are you fermenting long enough, right temps?
Do you leave your beer alone? Or do you take a bunch of hydrometer readings? (Personally, I don’t touch my beer for any reason for the full 3 weeks of primary).
How do you transfer your beer out of the fermenter?
How are you cleaning/washing bottles?
Do you steralize your priming sugar?
Sanitize your bottle caps?
All of your bottling equipment?
Somewhere there is a flaw in your process if your beer is undrinkable. I like the idea of finding an experienced brewer who makes good beer joining in and watching your process. Any local homebrew clubs?