На столе есть лампа. OK
В саду есть мужчина. In some context, it might work. Without context, it sounds a little bit strange, as if the man is permanently there.
В комнате есть два столи. Should be два стола (note the stress: столА) - genitive singular with 2, 3, 4.
В дом(a/е?) есть много окна. (is дома indeclinable?) 1) в доме (дома = at home, it is an adverb and is underclinable; дом = house, it is a noun: в доме = in the house) 2) много окон (genitive plural with quantifiers other than 1, 2, 3, 4).
В стакане есть некоторое молоко. "Некоторое молоко" means "a certain (kind of) milk". Just say: В стакане есть молоко. or В стакане есть немного молока (= a little milk, a small amount of milk). You do not need to translate English "some" into Russian every time.
В бюро есть много людей. In some context, it might work. Without context, it sounds a little bit strange, as if the people are permanently there.

В саду находится мужчина. OK
В бюро находятся много людей. OK Strange it may seem, but singular is also possible in this context, and it is even preferrable: В бюро находится много людей. The singular verb (находится) just denotes all the people being their as a single whole.