dissolve in cold water, ONLY THEN add hot water. The rationale behind it is that aromatics evaporate too quickly when the instant powder is infused with too/boiling hot water.
A tiny pinch of salt actually dulls the sharpness of a bitter coffee. Something something chemical reactions when salt mixes with coffee. Try it. It's great!
Based on experimenting with flavours but not this particular one yet, it doesn't hurt to try. Balancing the different flavour groups is an easy way to elevate meals (well, easy once you've calibrated your taste to be able to figure out what's "missing").
Just tried it and I'd say it's a positive difference, though I didn't spend much time searching for the "right" amount. With salt, I find it's better to err on the side of too little. Things tend to be ok with too little salt and yuck with too much.