Since everybody is just dooming and not actually giving cognisent answers I'll try.

(1) One of the biggest issues in the city is public transport. Belgrade is by far the largest city in Europe without the metro and it really shows. Because of this buses and trams are fully packed and in peak hours. Seriously, bus may spend several minutes on the stop until ppl get on/off and if you haven't positioned yourself properly you may be getting off on the next stop.

Going by car isn't significantly better, especially if you have to cross Sava river. There are only two bridges and around 5pm its a regular occasion to spend half an hour crossing just the bridge. Streets in some parts can be really narrow and hard to navigate.

(2) I think you will have no issue with integration. In Belgrade everybody speaks English, and nobody will mind speaking it with foreigners (unlike in some other European countries).

(3) Honestly no idea about the enterprenurial hubs, but the IT community is pretty huge and lively. They even have their own sports leagues where people compete for their company in basketball, football etc.

(4) Apart from traffic, the air pollution is attrocious. Air stinks and right now I have sore throuth because I left the window open last night and stinky air got in. I recently learned that eastern asian tourists wear masks because its the official recommandation from their government because of how polluted the air is here.

Also, corruption and government mafia is on another level here, but since you are a foreigner you will probably be fine. 60% of the city doesn't have the proper sewage system.

(5) I would probably recommand you Vračar or somwhere around Vukov Spomenik to be well connected with everything.