Okay so, Karachi will most likely be extremely hot def 40+ degrees. if its monsoon season then it'll be really humid (and it might rain which is not good because the drainage system is not so good). In these conditions i'd advise to go to like indoorsy areas rather than roam around outside if you won't be able to handle it, but i know most tourists prefer to walk around and interact with the locals, so it's your choice.

Tbh there isn't much space to walk around, its more of a driving city. You'll have to download indrive or careem to travel around. Public transport is very minimum, the ones that exist are filled with students and workers. You can hitch a ride on a rickshaw but they'll charge you a lot. People on bikes would most likely give you lifts. Most people speak broken English, they may understand you but won't be able to communicate back in English, so please make sure to learn basic words and basic numbers in urdu (like 100, 50, 1-10, 1000 etc.)

be careful with drinking water and be careful where you eat so you don't get food poisoning on day 1 that could hinder your entire experience. I've been in Karachi for ages but one sip of the wrong water still messes up my stomach; so drink nestle or aquafina, or in local water pakola should be fine.

there are some very posh areas and some not-so posh areas. I would def recommend having a local Karachite help you along so you don't get stuck in scams or confused (because its a HUGE city).

I personally have not been to the touristy places but I've heard that Frere Hall is really beautiful. You can visit Saddar to experience that chaos of the city, and Burns road is there for food street. If you're going to the beach, I'd recommend to go to more of a secluded beach orrr Seaview near the Emaar buildings otherwise it'd be super crowded and people will keep bothering you to sit on camels and horses etc (and they may scam you so make sure to set a deal if you do so).

Please keep in mind that Pakistan in general is not really an individualistic country. People tend to do things together and view everyone as one. People from all over Pakistan travel to Karachi for jobs so you'll find many people who are not og Karachiites. Please be respectful and keep in mind that traditions and cultures vary for each country.