So, this living card game is dead... but I write this post as a commentary and quasi-recommendation for those who might be in a similar situation as me.
A friend and I played Warhammer Invasion a couple of times in 2015 and I was immediately hooked. The rules are relatively simple, and the game-play is dynamic. A single strategy can't be employed for every game, meaning you have to think outside the box. Balance your resources. Work out how to best defend your zones.
Aware the game was being discontinued, I secured myself a copy of everything, and two years later I'm getting around to deck-building.
I've trawled through these forums and other websites for deck-building tips, endured the arguments about deck-size (Magic mindsets and probabilities) and have come up with the following. Remember: this isn't a guide to create the most highly competitive decks, but rather multiple balanced decks across the 10 factions (main 6 plus the 4 from Hidden Kingdoms) that you can consider "pre-built" to bring out at game days with mates.
60 cards per deck (to start with)
Exclusively use common clan cards, not the neutral cards (again, to start with) and not mixed clans
Choose quest and legend(s) cards that share some alignment with regard to strategy
3x same quest
3x same legend, or 2 pairs of 2 legends
Units, Supports and Tactics to directly support a small array (2-3) of structure/strategy from the legend/quest
50% (~30 cards) units, comprising:
7 pairs of "first turn cards" (cards that can be played with just 3 resources)
6 pairs of other units
3-4 cards being legends
25% (~15 cards) supports, comprising:
50-75% (6-12) of these being "first turn cards"
75% (10-12) being non-attachments, and ones that provide power
Again, mostly pairs of cards
25% (~15 cards) being tactics / quest
3x same quest
6 pairs of tactics (again, consider balance high and low cost cards)
Pairs of cards gives some degree of consistency (more than elusive single copies), but also provides more variety for casual play (rather than a competitive trimmed down 50-card deck with the max 3 copies of most effective cards). It will enable employing different strategies / game-play with the one deck.
As I've been looking through the cards with all of the above in mind, I'm identifying 2-3 straight-forward synergies between the cards within the clans to focus on, while avoiding situational cards and very specific combos. The above is just a starting point and, as the flavour of the deck dictates, may justify deviating from. e.g. a really crucial card that you might want to max to 3 copies. Or, in the case of Skaven, going with 3s instead of pairs because of the action letting you play for free copies of units already in play. Or increasing deck size to 75 in a high-mill deck.
Furthermore, once I get these decks in play (I plan to will host some sessions at our local gaming shop), if I discover any are lacking or significantly weaker than the rest, then I'll drop in the neutral cards to beef them up and/or directly complement the strategy of certain clans' decks.
If there's anyone still out there, would love your feedback and any other tips. And I will likely follow up to post the preliminary and then final lists up here for the benefit of others.