This holds true for pretty much all trees...
If the tree defoliates, as yours has, water ONLY when the soil is fairly dry. NOT bone dry, no, but when a chopstick/toothpick comes out clean. Under no circumstances should a tree in this condition be overwatered.
When healthy, different trees have different requirements. Some like to be kept "feet wet", and some will die if their roots are constantly wet. Some like to go completely dry between waterings, and others will be killed by this. For Elms, holding to the above, watering only when dry, is probably the best course.
As far as fertilizing goes, only an actively growing tree should be fertilized. I also prefer water soluble fertilizers. I like DynaGrow (7-9-5) at half strength, but have used others, never higher than 10-10-5, also at half strength. I fertilize weekly during growing season for actively growing trees. During the fall and winter, growth slows even for my indoor trees because they are subjected to shortening natural photoperiods and temperature drop in my garden window. So, during this slow growth period I fertilize only once per month.
As to how to water, you'll find as many different opinions as you'll find bonsai growers. The smart reader will KNOW that, from this, there can not be any one right and perfect way to water bonsai. What I can say is that anyone who tells you emphatically that one particular way is dead wrong, harmful, or deadly is probably a person who either has very little experience and is just regurgitating advice, or someone whose advice is suspect on probably most levels. That said, I can only say what has worked well for me. I soak all of my trees for half an hour per week in fertilized tap water (400ppm TDS), longer on newly repotted trees. I never water from the top. I mist twice daily, using distilled water, using approximately one quart per day. Have I lost trees? Of course, everyone's lost trees. Anyone who says they haven't hasn't been growing very long. Do I attribute any of these deaths to watering methods? Absolutely not. The trees I've lost have proven difficult for me (and many others) indoors, regardless of methods (which I have varied to test this theory). So, pick the method that works best for you. Try different methods. Change it up, and find an overall care program that works best for you.