Hi. I got my first tank when I was just a little younger than you (44 now). I am pretty new to corals myself, only about 2 years. I have a 36 gallon tank. I am far, far, far from a coral expert. But I will tell you what I have had good luck with, and not so good luck with.
First of all, how long has your tank been up and running? It is generally recommended that a tank be at least 6 months old before you start adding corals. This will allow some of the wild fluctuations in water chemistry to settle down. What is your filtration system? That will make a difference as well.
The corals I have had the best luck with are green star polyps, a creeping star (i'm sorry, I forget the name but it is spreading), blastomusa, frogspawn, duncans, Pavona/cactus/bird's nest, and a chalice called a Hollywood stunner. Duncans are persnickety buggers. They take a while to settle in. Be patient with them and don't move them around a lot. Put them in a low flowing area.
The ones I had a hard time with were acros, montipora, hydonophona. I would not try those, or try small frags once you have had some success with the others.
Zoas are pretty, and I have had pretty good luck with them, but be careful. They can be toxic.
I just read that you said low flow. My growth on some of the harder corals like pavona and the chalice really took off when I added more powerheads. They will also help with 'dead spots' where detritus and red algae can build up.
As for dosing, I regularly check kH, calcium, and magnesium along with salinity and pH. This is after my tank cycled and I have ammonia, nitrites, and nitrates where they are supposed to be (0, 0, and as close to 0 as possible). All of these are related and affect one another. I had a hard time getting my calcium up high enough without spiking my magnesium. Go slow and in the beginning, check often.
I don't know about your water source, but I strongly strongly recommend RODI water. It has made all the difference with this tank.
My advice is to treat your tank like a garden. Start with some small, inexpensive frags and see what does well. My chalice was a $10 frag the size of a nickel, and it's now about 3-4" across. Use the smaller frags to see what does well in your tank, and then slowly branch out to similar species.
Again, wait for more experienced folks to chime in as well. These are some of the ones that have worked (and not worked) for me.