IRL I like using 3, but no more than 2 of any one kind. More than that and analysis paralysis gets worse.
Question from a non-beginner, but certainly no where near an advanced player:
When referring to "kind", are you referring to event vs landmark or the nature of the card-shaped object?
If the latter, how do you categorize the different kinds?
For Landmarks:One-shot – Mountain Pass
Throughout, but limited duration – Arena, Basilica, Baths, Battlefield, Colonnade, Labyrinth; Aqueduct, Defiled Shrine
Throughout –Tomb
Only at end – Bandit Fort, Museum, Wall, Wolf Den; Triumphal Arch, Tower, Orchard, Obelisk
Treasure related at end - Fountain, Keep, Palace
For Events, I've got the following attributes for them...
Cost
+Buy
gain
VP
Trash (hand)
Trash (play)
draw
discard
limit
other $ restriction
token