Which ruling comes first: Combining prayers during rain or offering each prayer at its prescribed time?

Should the Imam be followed when joining prayers because of rain or this isn`t allowed for the praying person who doesn`t meet the conditions and rules of this concession?

Is joining prayers because of rain from Sunnah?

Is it permissible to combine Maghrib and `Isha` because of the curfew?

Is it permissible to combine Jumu`ah (i.e. Friday) and `Asr prayers due to the corona virus curfew?

Is it permissible to combine Duhr (Noon prayer) and Asr (Afternoon prayer) due to rain? And is combining them due to cold, snow or heavy rain permissible?

If I`m making Jam` Ta`khir {Delayed combination} of Thuhr and `Asr, what is the ruling on offering them in sequence?

Is it permissible to combine prayers in the mosque because of heavy dust, mud, and wind, similar to rain, knowing that dust could be more harmful than rain?

What is the ruling on joining Zuhr and `Asr, and Maghrib and Isha` because of sickness?

According to Shafie jurists, the distance which permits a traveler to shorten prayer is (48 miles), and a mile is about (6000 cubits). Therefore, how many kilometers is the cubit and the mile according to the reliable position of the Shafie jurists?

While combining prayers, is it permissible for a person to leave the Masjid to run an errand, after performing Duhr (Noon) for instance, and return afterwards to catch the second Rakah of Asr (Afternoon) prayer?