The “out” party (relative to the White House) chooses the week and they go first. The “out” party often chooses the end of August because it gives them more time to get their act together after a typical bruising primary struggle. It also forces the incumbent party the hassle of having to wait until after Labor Day, when people are busier with their own lives, football season and school have begun, etc.
Cities compete for the privilege of hosting. I don’t remember who competed w Tampa. I know the Dems had to choose between Cleveland and Charlotte and they made a HORRIBLE decision, as it turned out.
Dems considered Cleveland, St Louis and Minneapolis in addition to the "winner" Charlotte.