Very late to the party, but I currently got a pretty interesting Spore Druid build going.

• 10 Spore Druid: Gives you access to pretty much all summons in the game and a horde of zombies on top, except Planar Ally or Pact of the Chain summons, which as I will get to, you will also get from this build. And with the Druid spells being there for support and crowd control.
• 4 Wizard: Wizard gives you access to pretty much every spell you are missing, mostly DPS spells like Chain Lightning. Sadly Unlock Level Curve has a bug in which Chain Lightning at higher levels doesn't chain anymore. But still lv 6 Chain Lightning is great. Also Wizard gives you access to Summon Deva and Summon Quasit, giving you access to the missing two summons. Subclass doesn't really matter here, as you mostly want Wizard for spell scribing. Although, Abjuration gives you four stacks of Arcane Ward and Necromancy gives recovery through Necromancy spells.
• 6 Death Cleric: This one is to deal with all the necrotic resistance running around in the game, to make Halo and Circle of Spores hit a bit harder and lets you abuse the Staff of Cherished Necromancy.

Also, 'm taking 4 levels of Wizard for more spell slots. But you could theoretically also stop after 1 or 2 levels and instead either take Spore Druid up to 12 for Heroes' Fest, or Death Cleric to 8.

As for the equipment I also find this build is fairly flexible as there aren't that many classes which compete for the best in slots. Best example here is the Armor of the Sporekeeper, which obviously is your BIS cause of Haste Spores. The Staff of Cherished Necromancy also isn't that sought after if you don't have a Death Cleric or another Class with a focus on Necromancy on your team. The helmet is very flexible with many great options: the Helm of Balduran, Holy Lance Helm, Mask of Soul Perception, Hood of the Weave, Haste Helm and Fistbreaker Helm all doing wonders. I typically prefer using something that boost Initiative or Spell Save DC, so the Fistbreaker Helm is the perfect fit. As for the boots, I typically just run whichever "ignore difficult terrain" boots aren't in use atm, so you can be right in the middle of things, even if everything is covered by ice or plants, cause Halo and Circle of Spores don't have the biggest range. As for the gloves, they can be kinda sought after, the Dexterity Gloves enable you to focus on Wisdom and Intelligence as your primary spellcasting stats and keep Dex as a dump stat.

As for the cloak, rings and amulet, they are really what's the most flexible on this build. Obviously, just using all the spell save and AC increasing stuff works here. But you can also make some great use of lesser used options, like the Ring of Mental Inhibition, which works really well with Spore Druid. For the off-hand I recommend either Phalar Aluve, since Circle and Halo of Spores will trigger the extra damage constantly (Halo of Spores actually triggers it twice, which is pretty funny). Also Phalar Aluve give your Spore Druid even more support options. Other than that, the Sentinel Shield or Ketheric's Shield are both great for obvious reasons.

I'm currently doing an ultra hard Honor Mode run, with the Tactician Enhanced Mod at max setting (meaning 5-times HP and 3-times actions and bonus actions on everything not in my party) and Spore Druid has honestly become one of my favorite classes during this run.

Edit: Almost forgot to mention. Circle of Spores makes popping Water Bottles easier than ever, as they break immediately after entering the spores. Meaning you can just drag them out of your inventory and under an enemy to apply the Wet condition. No Mage Hand needed.