The amount of watering a tree needs is dictated by just that... need...
You need to keep it moist but not wet... the way a tree takes up moisture is by vapor exchange in the soil... it does not suck up water itself. If the soil is too wet, then there is no vapor to absorb, and the tree will dehydrate because it can't take up the water. Then the roots will rot and die as well. This is also why a light and airy soil mixture becomes important when you get further along and come to a point when you have to repot it.
When you are checking soil moisture be sure to probe a little bit as the soil beneath the surface can sometimes be drier than the top. Especially if there is any fog/mist/rain that touches the soil surface but doesn't penetrate.
When watering make sure you water until the tree is freely running water out the bottom, then make sure it can drain throughly. Often times when teaching people about watering I'll tell them water throughly three times... once for the tree, the pot, and the soil. The reason being is that the soil will absorb a little more water with each watering. Soil that is dried out can't hold as much water, as soil that is already moist. Which is why in the "emergency care" threads on here you'll see references to dunking the trees in a tub of water... it's to rehydrate the soil... not the tree.
Also if you think you've overshot your watering window and the tree is a bit dry, misting the foilage is also a good measure as foliage can take in a certain amount of water.
Watering is the most important factor of keeping bonsai alive. The discipline of it can be the most difficult for people to master because there is no such thing as "doing it tomorrow" if the soil is dried out. I have about 100 trees, and believe me, there are days when it's a chore with twice a day watering.
My second concern is the amount of light your tree will get on that screen in porch. Because you don't have a heavy winter, and because it's a needle juniper, there will always be a certain amount of growth activity going on. As much light as you can let it have right now is also critical to it's health. Keep in mind that you'll want to protect it from blistering sunlight in the hotter times of year. But for the moment, please make sure it's in the sunniest part of the porch.
As to feeding, while junipers are acid loving, I'd alternate between regular Mircale Grow and Miracid during the active growing season. There is a certain amount of acid naturally occuring in soil, so you don't have to feed it Miracid each time. And it is not needed at this time of year, because the growth will be slow.
Given where you live this tree should grow like a fiend.
Enjoy! And welcome to the hobby of a lifetime.
La belle cose prendono tempo... (Beautiful things take time...)