Forging a new "Wald"

https://www.worldanvil.com/w/alderwald-symbolicm

I am Inexperienced at world-building but I'm diving in headfirst. My RPG background was MERPS and a touch of Paranoia back in my "yoof" but I've never attempted to create a campaign world like I am trying to establish now for my kids and long-distance friends.

My goal is to convert multiple magic the gathering custom build decks into an ACKS campaign world capable of zooming out to table top battles with the (free) Domains at war set.

I know there are a lot of resources available on youtube for worldbuilding which I am wading through, but I'm struggling with a couple of issues at the moment  that I don't think I'll get ACKS relevant answers to anywhere else.

I'm basing much of the campaign world on the Kamigowah MtG block set along with Some Guildpact.  

I have Core Rules, Player Handbook and Sinister Stone to my name but I feel it is a little lite on the mechanics of dealing with spirits, having stats for Invisible Stakers, Spectres, Shadows and Wraiths between them. How much would "Lairs & Encounters" aid me in compiling a benevolent/malevolent spirit predominant campaign world?

I want to emulate the MtG splice onto Arcane mechanic. Is there a homebrew system in existence that I can crib?

I'm petty sure I will be able to muddle through with the resources I've got but if you are further down the road on this journey than I am I would very much like to sit at your feet for a while and listen.

I have Core Rules, Player Handbook and Sinister Stone to my name but I feel it is a little lite on the mechanics of dealing with spirits, having stats for Invisible Stakers, Spectres, Shadows and Wraiths between them. How much would “Lairs & Encounters” aid me in compiling a benevolent/malevolent spirit predominant campaign world?

You’d probably find Heroic Fantasy Handbook to be the most useful to you, in that it has rules for ceremonial magic, cacodemons, black and white magic, and other stuff. Lairs & Encounters does add some new undead types, too, although spirits aren’t its focus.