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I like your chapter idea, however I am not a fan of the idea to paint up some Chaos dudes and call them Loyalists.
Your chapter concept seems kinda dark (which is totally cool) but I feel that you may find, in the end, that they simply look like a chaos army.

If I were you I would consider kit-bashing between regular and chaos marines and cut away/file off any obvious chaos insignia.

Something else you may consider (as Chef of Cadia mentioned) is looking into 3rd party bits. Do not forget about Forgeworld either.
I feel like the Sons of Horus kits may be right up your ally as far as spikiness is concerned

I hope this helps