Generally speaking, your tattoos won't effect your visit to Japan (I say this as a Japanese person who migrated to the UK).

There's a big difference in appearance between the Yakuza and tourists (who are generally Caucasian), and while people may stare they certainly won't harass or arrest you for having a tattoos.

In temples you might be expected to cover your tattoos depending, and you definitely won't be able to visit an onsen (at least none that i know of).

In terms of what changed for me when I got my sleeve - nothing that was bad! Personally my confidence soared after I got my sleeve. I find people looking at my tattoos, but that's to be expected so as long as that won't bother you, go ahead