Exactly. Using a 1,5% stop is fine, even for staining developers. 15g/ltr. Citric Acid in 1 ltr. water.
Most commercial stops have an indicator from Yellow to Blue (pH > 5,5). 1+19 - 1+29.
Water will not stop developing, only it slows down the process. A stop immediately stops the developing process and you have less contamination of the fixer. For an Acid type fix you can leave the stop but for an Alkaline fix you need a stop.

About lifetime of the stop: You can re-use it many times. One liter maybe 15-20 films but with Citric Acid you need to take care you have no bacterial grow in the stop when it stays for a long time.
With developers containing high amounts of Carbonates in theory you could have some degassing on the film surface but I never had any problem with any film. Even the so called problematic films like Foma and Efke, softer emulsions and often reclamations on pin holes did not show any probems for the last 12 years which I am using Fomapan (35mm and 120 roll -) films from the Czech Republic.