No need to flush now, I'd just stop with the nutes for a week or 2. Most people when they grow soil don't even start with the nutes until flowering. Most soils have enough nutrients to go for about 2-4 weeks after each transplant before its starts to become necessary to add ferts(this can change depending on if its a time release fert soil, such as MG 3-6 months.) You've also got some kind of ferts in there already (little yellow pellets that tevfik recommended you remove.)

As far as watering, lift the pot when completely dry and then lift it when you just watered. This is the method most use for determining if they need to water or not. I still use this method with my 3 gal pots.:thumbsup::thumbsup: