You never want to add any type additive every time you water,the soil needs time to process the molasses,if not given enough time it ends up being worse than adding nothing at all,the actual plant uses very little if anything from the mollases,its main benifit is from feeding the organisims within the soil,you only want to use molasses every few weeks & when using keep the amounts small,like about 4 or 5 spoonfull per gallon.
As for watering you should wait until the soil is dry before you water,when you do water you want to flood the plant until water flows from the bottom,let it sit a half hour & water heavily again,this assures no dry spots in the soil & pulls fresh oxygen through the soil as well.
To know if the plant needs water takes paying attention to several things,first you scarify the top inch of the soil using your fingers,the top inch should be loosened by scratching around in the soil,scarifying the soil helps the soil stay loose & it also helps with parasites,when you scarify any larve living within the soil get brought to the surface where they dry out & die,it also helps you feel moisture in the soil.
After loosening the top in inch of soil stick your finger deep into the soil,try & feel any moisture in the soil,if it feels cold or very cool most likely its still wet,you want the soil to feel dry & about as warm as your other fingers that are not in the soil.
You can also tell by how heavy/light the pot feels when you pick it up.
Underwatering is very rarely a concern,the bottom of the pot stays wet for days & most new growers overwater,underwatering is very easy to spot,on day the leaves look normal & the very next day all the largest leaves will droop,your far better to be very cautious & water only when your sure its dry than to constantly over water.
The next time you think it needs water wait an extra day or 3 before watering,pay attention to the leaves,if after waiting a few extra days the leaves are not showing signs of thirst then you've surely been over watering & should cut back on the water,im not saying you want the leaves to droop but waiting the extra 3 days will show you something,a thirsty plant cant go 3 days without drooping,now you know how much over watering has been going on.