Your Val should be ok with a standard dose of Fourish Excel, it may not handle a double or triple dose as a shock dose - I dose 7ml in a 64l tank daily and it is fine, but be careful, what works for some does not work for others, and mine is far from a 'normal' tank.
Corydoras do not like high doses of ferts, lost a few young'uns that way :oops:
Your Cabomba should be a good top cover plant, when it gets too long pull it out, chop it down by half and replant the tops - this works for Heteranthera zosterifolia as well if you don't want it to look terrible when you trim it down and have to wait for it to grow out again to look good.
Bit puzzled by this?
What temps you running the tank at?
As for the staghorn, Phoenix44 had some a wee while ago, see if you can find the thread by using the search function.