A couple questions for people who know what they're doing

Hello! I'm planning on starting a 30K army, and I just want a couple things cleared up to help me on my way

First of all, is there any gameplay differences between different Armor marks? I understand that lore-wise there are certain things (Mark III is the most durable, Mark VI is the most stealthy, etc.) but I assume in the gameplay there is no difference between a mark III squad and a Mark IV squad save the weapons they carry, but I would like that confirmed

Second of all, from what I gathered only certain Baneblade variants can be used for space marines, so -again- could one of you kind people who have more experience with the rules clarify which if any can be used by a space marine list?

Thanks in advance!

Hello! I'm planning on starting a 30K army, and I just want a couple things cleared up to help me on my way

First of all, is there any gameplay differences between different Armor marks? I understand that lore-wise there are certain things (Mark III is the most durable, Mark VI is the most stealthy, etc.) but I assume in the gameplay there is no difference between a mark III squad and a Mark IV squad save the weapons they carry, but I would like that confirmed

Second of all, from what I gathered only certain Baneblade variants can be used for space marines, so -again- could one of you kind people who have more experience with the rules clarify which if any can be used by a space marine list?

Thanks in advance!