I am trying to understand universe selection when running live.

I want to support "quick starts" for debugging purposes, i.e. basically starting up my algo (which ordinarily trades at start of day) and treat the current time as the start of day if exchanges are open. In addition, I want to be able to start it after midnight (during which universe selection ordinarily occurs, if my understanding is correct), but before market opens and have a selected universe. All of this is because it's very improductive to sit around and wait a day or more when trying to figure out why live version is running differently than backtest.

Secondly, how does the limit on number of securities mix with universe selection? Besides that, I haven't found a place that lists the number of securities possible for each resolution and instance type (aside form when ordering, but one needs to know about it earlier than that). It would be very useful to have a matrix somewhere that listed instance type versus resolution for supported number of securities.