Hello
I have had two sets of memoirs published by a small publishing house with whom I dealt direct. They were niche publications with a specific audience (although I always fancied they would have had a wider appeal if they'd had a marketing budget behind them). And, to be fair, one of them did win a literary award, Lakeland Book of the Year.
Now I am embarking on a novel which I am even more sure has commercial appeal. Should I pitch direct to large publishers or find an agent and should I wait until I have finished the book or start looking now?
Finish the book first! Then find an agent.
Most submissions ask for the first three chapters. If an agent likes that, they will ask to read the whole thing. It kind of annoys them if you have to admit that there isn't a whole novel. And by the time you've finished it, they might have gone off the boil...