Can stimulus packages lead to hyperinflation?
No chance. The economy is heading for a deep recession, because of an exogenous fall in demand (think of a supply and demand graph, where demand falls drastically, and so Q and P falls). Recessions most of the time mean less inflation (firms sell less). Exceptions are called stagflation and are fairly uncommon, except in totally destroyed economies where inflation is a deep cause of the recession, like in Venezuela.


numbers are most likely calculated by looking at needs, size of market, etc. In most cases these stimulus are funds. They are money to be put in a box and taken as needed. Not all might be used.
a lot of funds are targeted and not given directly as cash to people. In any case, people won't be spending the money as crazy, partly because there is little on which to spend it (no eat out, no holidays). Plus all the uncertainty about how long this will last make people averse to spend it. Wage costs are low and partly subsidized too so firms won't increase prices.