There are many more qualified opinions than mine on this but I have learned that Trimec has to be on at least 24 hours to be effective. That said it first has to be applied under optimal conditions. Trimec is only effective as it sits on the weed. If the lawn was dry when applied then you will not see much in the form of dead weeds. A heavy morning dew is the best as the droplets are small and the trimec can adhere and dry on the weed.
I applied granular on a day when there was dew and no chance of rain (so they said). It rained the same night and I had to go back and spot spray with a backpack sprayer. The fertilizer part worked great but the weeds needed the liquid hit to knock them out.
I can't help you much with Q2 as I am looking into a bigger sprayer myself. One hint - check with your insurance carrier to see if you have to increase your coverage for spraying as you can get into some trouble if things aren't done right. Good Luck.