1)- Nice to meet you!
- You too!
- Why don’t we use “ me too!” here? Because we are shortening 'And it is nice to meet you too!'
2) You’re here on business or pleasure?
- Can I use “for” instead of “on”? I'd say 'for' is better as for business or for pleasure both sound ok, but when you use on business (ok) you are also including 'on pleasure' which sounds quite odd.
3) We gotta buy some stuffs on the way home.
- Is this natural? Only if you say stuff instead of stuffs (stuff is non-countable as it means a collection of items and if you bought more than one collection of items it would all just combine into a single bigger collection of items).
4) I try my best to point out our ups and downs.
- What do “ups” and “downs” mean in this sentence? Hard to say without context. It usually means good times and bad times - possibly a company's financial ups and downs, or a relationships emotional ups and downs...
5) I didn’t mean to come off as defensive.
- What does “come off” mean in this sentence? 'Appear to you as'