MTG

You could consider

Card draw

Dig Through Time

Treasure Cruise

Id personally cut down to maybe 36 lands and add a few mana rocks in. Definitely at least a Sol Ring

EDHRec is a good reference for what other cards people are running and synergise well

edit - for the specific theme of abusing gandalf commander damage, ghostly flicker and other similar cards so you can reuse the “choose one not chosen”

rule clarification

The phrase "that hasn't been chosen" refers only to that specific Gandalf the Grey. If Gandalf the Grey leaves the battlefield (possibly because of the fourth mode of its ability) and then returns to the battlefield later, it will be a new object with no memory of the modes chosen when it was last on the battlefield.

edit as another comment has mentioned, Gandalfs 3 damage pings don’t count for commander damage

https://draftsim.com/mtg-commander-damage/

Commander damage is a pretty simple rule. When your commander hits a player for combat damage (i.e., only during combat when the commander is attacking and is unblocked), note how much damage that player has taken from your commander. If a player has been dealt 21 or morecombat damage over the course of the game, they lose.

I might be misreading your gameplan, but just in case: Commander damage only counts combat damage. So accumulating 21 damage on an opponent by attacking with your commander.

Gandalfs 3 damage do not count into that.

If you have cost reduction in your deck, Clockspinning

https://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=109673

Is one of my favorites for counters, it's one at a time but easy mana dump and works to add or remove one of any counter

Also, Vadrik astral archmage

https://edhrec.com/commanders/vadrik-astral-archmage

Is absurd with buyback cards since cost reduction is the final modifier.

Sorry if you already have these in your deck, I couldn't look since I'm at work

So Gandalf's damage ability doesn't count towards commander damage. Commander damage is only from when a commander deals combat damage to a player via attacking.

You want the cheapo hard counters like Arcane Denial, Dispel, Mental Misstep, Red (or blue) Elemental Blast, etc. Basically, counters in EDH can be rather subpar because you have multiple opponents and you're 1-for-1'ing. You and the owner of the countered spell are each down a card, while the other players are the same. They means you want them to be cheap or have draw/replacement effects on them. tl;dr-- holy fuck get rid of that Cancel it hurts my eyes.

For draw spells, there's Treasure Cruise, Gitaxian Probe, Brainstorm, Ponder, Preordain, Windfall, Prosperity, Narset Parter of Veils, Lorien Revealed, Frantic Search, and some others I'm forgetting. One trick is to combine Ponder and Brainstorm with a shuffle effect from cards like Merchant Scroll and Scalding Tarn to act as an Ancestral Recall.

And for fuck's sake where is you Command Tower and Sol Ring? That's how every deck in EDH should start lol. Both have been printed into oblivion so you should buy them for dirt cheap. Go do that. Like right now before you do anything else Magic related. Hell, someone might just give you one if you ask nicely.