How many objects can it handle and query, to ensure response is within 100ms?

We have a Google group https://groups.google.com/forum/#!forum/spatialite-users for asking questions.
It is also impossible to give an exact answer "SpatiaLite can deliver xxxx features within 100 ms". There are too many variables affecting the speed:  hardware, size of the features, if SQLite db is cached by the operating system..."

it depends on so many variables that the question is nonsense

hint: just write a simple test program and check by yourself your data on your HW in order to obtain a reasonable extimate