I think you'll find the coop has a floor. Without nest box, it is about 2' x 2' in the coop itsef. That isn't enough room for food or water and 3 chickens. Remember that the rule of thumb is 4 sq ft per bird in the coop of functional floor space, not including food, water and nest. That's not written in stone, but worth considering. In summer, if the coop isn't just as cool as the outdoors and have a breeze, they will want to sleep in the run. Chickens tolerate cold quite well but have a lot of trouble with heat. In that coop, if I decided to keep 3 chickens in it, I would use the nest area as part of the coop, and set something like a covered kitty litter pan outdoors for the nest (they only neeed one.) Food and water can go indoors or out for adults. Adult chickens do not eat or drink af night, but they do start looking for food and drink at the crack of dawn. The food needs to be kept dry which can be difficult if it is outdoors, even under a coop. Rain blowing in from the side can be enough to cause problems.
When I brooded indoors, I used a large refrigerator box resting on a large sheet of painter's plastic, with a heat lamp very carefully and safely suspended from a rig on the back of a heavy chair. I put a standard feeder and waterer on bricks. It can be done without spending a bunch of money.
They will only need heat for a very few weeks, particularly in your climate. You will find they don't like things as hot as the charts say and can easily be weaned off heat entirely at 3 or 4 weeks. The Eco Glo is a lovely product but you may not get much use out of it.