Some more ideas and input on the fox matchup.
You can catch a lot of fox aproaches with well timed uptilts and upsmashes or cc dsmashes. Try to do nairs and land behind him then do some OoS option quickly as most foxes do(they tend to have bad patience) and you will be able to land a hit. FJ nairs are great IMO vs fox, they can give you kills out of nothing, when spaced correctly they can't really hit you and you get a lot of mind games from them, double nair, DJ fair, DJ nair, upair, and crossovers, and a fox will not like to jump into it as it will screw up their pacing and give you a window of momentum and a chance to go for a combo.
Fairs are great, don't trade them, its a spacing tool, and thus you should use that range (just about the same range as marths fair, just not as quick and covering as much, still a good move) to outrange your opponent with them. A traded fair is generally a failed fair against any character but marth and ganon. Fairs leads to combos and kills, you should use them IMO.
Also use jabs, they have the same benefit as nairs to mess with a fox's pacing, catch him as he jumps and his other inputs is a screw up which you can punish. Catch him as he lands and he might go into shield from a failed L-cancel.
And the most important, your punish game must be extreme, link has the potential to convert a hit to a kill vs fox, you must use that potential. You cannot pressure the fox, but he will screw up, even the best fox does do mistakes, and when he does, it must hurt.
Bomb to forward smash can be don OoS and is to me highly relieable as it is a safe try, bomb connects you get 45% bomb doesn't and you can respace get a new position and breath for a little while. Bomb OoS will be your best defensive option the whole match.
Basically this is a tough matchup to learn, but also one of the most satisfying matchups to win when you know it, it kinda makes link look top tier, though he isn't, when you do.