How many equipment can I equip to 1 unit?

Yes, you can equip as many equipment cards as you want to a single unit. There is no limit.

Per FAQ 9165 (and confirmed by Rule 818.3.b), a unit is "Equipped" as long as one or more of its attached cards are Equipment — and no rule restricts the number. As long as you can pay each Equip cost and the gear isn't already attached (you can't activate the Equip ability of already-attached gear per Rule 730), you can keep equipping more. Each separate piece of gear is a separate activated ability, so you can activate them one after another during your Main Phase with an empty Chain and no Showdown.