Is it safe to sell old equipment or....

[Maniak 2000]

...it is required for quests or item crafting?

[Seraphita]

I wonder exactly the same. I fear selling anything in case. I know one of my armors used another piece of armor I had with me to make it. Sooo this might be a hint. What to keep or not, though?

[∞]

Don't sell anything especially if you're trying to get "World's Biggest Welch Fan" and "Dutiful Deliverer" achievements. Keep them, you will need those later on.

[Radiosity]

Yep, most items are useful. Just multi-kill enemies for battle board bonuses, that'll bump your money after fights. Later on there's a method for grinding insane (like millions) amounts of Fol when you actually want to start doing serious crafting.

Later in the game, you'll get access to the ability to improve equipment as well, that requires other pieces of equipment as part of the process. So yeah, don't sell stuff.

[Maniak 2000]

Thanks all. Will keep it then, in most Jrpgs it's pretty safe to sell old stuff.