Short answer about dilutions:
Undiluted: nice tonality, minimum grain, lowest sharpness of these three
1:1: nicer tonality (in my opinion), less grain, greater sharpness
1:3: nice tonality (in my opinion), worst grain of these three, maximum sharpness of these three
As for a presoak, I haven't found it to be necessary but some do. Bear in mind that you'll need a slightly shorter development time if you presoak, because the film starts developing quicker. One minute at developer temperature should be good; I wouldn't use warmer or colder water because you could reticulate the emulsion. (It's not likely but it's possible.)