How Alpaca handle/implemented stop price functionality in stop-limit order

I want to know how fast Alpaca handle stop price thing and what is the market data source they use to know if stop price is reached?

For example let say AAPL current price is 119.98.
And I place a stop-limit BUY order with stop price 120.00 and limit price as 120.01.
So my question is:
How Alpaca would know when price reached 120? Is it done via SIP feed? How do they filter wrong/late reported trades?
What is the latency internally in Alpaca from the point stop price is reached to the point order is placed for execution at limit price?

Basically I want to know if stop-limit order will work as expected when stop price and limit price are very close and market is moving?

If I place AAPL stop-limit order with stop price as 120.00 and limit price as 120.00, how likely it will fill in normal market condition?

What is the advantage of using stop-limit order instead if I listen to SIP feed myself and then just place limit order myself. Is it just the latency between client(me) and alpaca overhead? Or is Alpaca handling stop price in some special way?