Briess has really hard water and it shows up in their extracts. For Briess extract I would use only RO water.
Munton's, I'm not sure their water quality but it is presumably "better".
For extract brews, I'd only add gypsum if brewing an IPA. Otherwise 90% of the time I wouldn't add any salts.
For a recipe.... hang on, I'll update in a few minutes.........
EDIT: OK, here's a couple favorites of mine, turn out great every time...
NOTE: If you want to brew 2.5 gallons, just cut the ingredients in half or whatever. Easy to do.
And a bonus: