Yes, we will say: я понимаю.😌 Но: видишь!?☝🤔

Я вижу. - I see where you are pointing. Я вижу, куда ты клонишь. - I see/ I understand what you mean. But usually we don't use Я вижу in the meaning Я понимаю.

No, you can't say "Я вижу" as "Я понимаю", but you can use "видишь ли" as "you see" when you explain something to someone. So "видеть" means "to understand" in some way. Let me give you an example. "Видишь ли, все не так просто" = "You see, it's not that easy" (you're trying to get someone to understand your point) I hope this helps!

I would say - no, I mean if somebody tells or explains you something you can not say я вижу where in English it would be very natural.