Gregory's Server
1/2 I think you won’t know if sign-ups are generated following a visit to joinmastodon. It would require some callback or ping to a stat server at the end of the subscribe process, which won’t likely happen impossible unless a Mastodon setting allows instance to ping joinmastodon back.
Generally, starting with metrics means entering a loop of measurement, refining, analyse, measurement… which is costly and – personal opinion – should be avoided on rather simple UI / user journeys.