I find that the trace mix sometimes get mouldy if not kept in the fridge (or not acidified with something like hydrochloric acid).
The macronutrient mix, consisting of only salts, is fine unrefrigerated.
Not in particular; I suppose if you have too much nutrients in relation to the amount of lighting you have, it could cause (algal) issues.
I've noticed the algal issues really increased when I started dosing Excel in the non-CO2 Tanks. And by increased, I mean I have to scrape the glass a bit every other week. Still balancing the light / CO2 / Ferts thing right now.
Getting better. No monster algae issues - except the crapola hanging off of my now-trashed Java Ferns. Hate those things anyway.
All else is good. The Plecos, Amanos and Otos are doing a good job, as well as managing the light better.