I agree with Slice, don't stress over numbers. STOP using the pH buffer. Testing the pH right after you've used the buffer is not going to give you an accurate reading. You need to test 12-24 hours after the buffer was introduced.
Testing your pH first thing in the morning will give you the lowest reading. As your lights are on throughout the day, the pH will rise. The goal is to not have too much of a difference in the low and high number. For new aquarium setups, I recommend that you test the pH 3 times throughout the day to get an accurate measurement of what your pH is doing throughout the day. Test once first thing in the morning when the lights are first on, or just about to go on, then again in the middle of the light cycle and then once right before they go out or right after they go out. If the three numbers are consistently close, no worries. Mine goes from 8-8.15, but I also have a refugium to keep things in balance.
The API kit is tough to read, in time, invest in a pH probe, they're easier and more accurate. For the API card, as long as you're in the color range on it, and it's consistently the same color, or close to the same color, leave it be. I wouldn't be buffering a new system.
Don't stress about the Ca, in time, if you add corals, you'll wish you still had that number or close to that number.
As for the temp, I'm not a fan of Marineland heaters (Really not a fan of Marineland anything to be honest), but it's what you have. Turn the dial up a little and let it go for a day and see what you get. 77-80 is the range you want to be in, but consistency is what matters. As long as you're getting a stable temperature, RELAX. If it's 76 this morning and 80 this afternoon, that's when you need to start stressing.
