i can't tell you 100% that nothing will happen (because there are stupid people everywhere) but i think you don't need to worry in general about the safety.
as afrouli said you should visit Ada Ciganlija for a walk along the water. Also i think you will like the food. Not from belgrade so i can't really recommend a place.
Just got home from my vacation but heard that taxis are on strike because of some stupidity with cargo (kind of uber) so i think it is a bit crazy traffic in the town.
tanks and cannons are a part of a military museum located at the fortress. was not there for a loong loong time but as i remember there are exhibits of military stuff from old old days until now.
What are you doing in Belgrade? How long are you there?
I have been told to go to Skardaska and check out the food there, as well as along the river under the fortress. I am hoping I have a chance for some tourist activity.
Yes, it would have been nice if the hotel let me know :) I tried Cargo, no luck there either. Ended up find a cab but it took about an hour all up.
I am here for work for a few days which means it is always hectic and unpredictable. I have always hoped to organise some kinds of meetups but it is not really possible with the schedules :/