JHCCoffee all down to your own taste and experiment but I have found my preferred results for lighter roasts to be contrary to what the general recommendations seem to be. To dial in, I generally look for first drops after 8-10 seconds on preinfusion, and aim for the below shot time. Shot time can be up to 35 seconds depending on the bean for me.
The following is approximately what I’ve done with most lighter roasts lately:
18/18.5g in depending on bean
34g out in 30 seconds
Beans rested minimum 2.5/3 weeks
That has given me my preferred results but that may not work for you. I pretty much always stick with that kind of ratio no matter what the roast level - I don’t know why, just me! I will go a bit more sometimes but mostly it’s that. I will dose less sometimes with a darker roast but the extraction (bottomless pf) generally indicates if that needs to change. Anyway, start with your plan above and change as you think one variable at a time, have fun and hopefully don’t sink too many shots!!