How's my tank?

Sharks get pretty big though and with gouramis you need at least 2

CO2 is a bit on the high side. I wouldn't panic yet unless your fish are acting eratic. Since it's the Hagen system you have no real control over the output so I'd suggest adding some surface turbulence to get CO2 to ~30ppm.

I'd add another gourami if you can get a male/female pair otherwise they may get aggressive to each other.

Yeah, I wouldn't stress, I've been up that high with DIY and no adverse effect, unless you include lots of pruning. OTOH, your yeast batch will die off that much sooner with the higher output. Be ready to mix up a new batch within a week, probably less. I wouldn't want to maintain that level for too long, but recall that the pH-KH-CO2 relationship gives you an upper estimate, only truly accurate if all your KH is from carbonate species. But then, CO2 is fairly insensitive to KH anyway. Try entering a KH of 10ppm lower and see what it reads, that's what I do and figure that my pH is somewhere in that range. I also do a +/- 0.1 on pH, but that's just because I'm usually around 6.7 (I guess) and it's nigh impossible to tell between 6.6 and 6.8 on the test kit.