Enhanced defense/weapon stacks with previous Magic item? How does the Mark Magic for multiclass?

hey dude, two questions…

1.Enhanced defense/weapon stacks with previous Magic item?

2. How does the Mark Magic for multiclass? Both? (I ask because spellcaster level)
1. Infusions can only be used on nonmagical items.

2. Spells of the Mark are additions to any spellcasting class spell list you have. The levels listed are spell level.

— Dan Dillon 👥 (@Dan_Dillon_1) November 21, 2019