i've had my belly button pierced before. 1-10 it was a 1 at most but everyone's pain tolerence is different.
Some advice for you
go in thinking it will hurt and it will, think it won't and it won't. Pain is just temporary and as soon as it's done it won't hurt at all if it even hurt in the first place.
belly button rings are notoreous for getting infected because of where they are. Make sure to follow the cleaning instructions from your piercer. H2ocean 3 times a day and NO MORE! cleaning to much can actually cause it to get infected. Wear loose clothing so as not to irritate it. DO NOT touch it with your hands. Clean it with qutips.
Hurts about 4-5, like it hurts but it's a piercing. What do you expect? haha
But yeah, it doesn't hurt as much as people say it does but everyone has a different pain tolerance. I think belly button piercings look good on the right person, not being funny but don't get one if your overweight because in my opinion they can never be pulled off. Piercings are kinda supposed to attract attention to your best features. Good luck and look after the piercing and be prepared that the pain of the piercing may not be the most painful part of having a belly button piercing, so prone to infection.
i'm not a guy, so I can't really speak for them, but I have heard good things. some guys really like piercings, and others are turned off, it's pretty subjective. it is known to be somewhat popular with males.
the pain is quick, I would compare it to biting your tongue, it's not absolutely awful, but it hurts for a second, it pulses for a little bit and you're good. it's over very quickly and isn't something to be nervous about.
after the piercing, keep it clean, wash with sea salt, and be sure to rinse the sea salt off. [some people don't know that, piercers think it's obvious [as do i], but I have had too many friends who don't wash it off, and they get burns].
Obviously it hurts. A needle is being shoved through your skin. But the pain won't last long.