Is it permissible for a worshiper to say the taslim before the imam? Do movement, laughter, and speech invalidate wudu’ as they invalidate prayer? Is it permissible to wipe over leather socks (khuffayn) if they have a hole smaller than the size of a toe?

Congregational prayer is not sunnah for the regular supererogatory prayers (rawatib) or other supererogatory prayers, but it is permissible. The preferred approach for voluntary prayers is to perform them individually, except for specific ones like the Eid prayer, the eclipse prayer, the prayer for rain (Istisqa'), and Tarawih. It is permissible for someone performing a supererogatory prayer (mutanaffil) to follow an Imam performing a fard (obligatory) prayer, but it is better for the mutanaffil not to leave the Imam's prayer before he finishes. Laughter during prayer invalidates it, but the correct view is that it does not nullify ablution (wudu') because it is not an impurity (hadath), and what does not nullify wudu' outside of prayer does not nullify it inside of prayer.