QIf my field has reached its card limit, and I have a Magic Sediment with 1 Stack counter on my field, can I use it to pay the cost of this follower's activated ability "Summon a Guardform Golem or Strikeform Golem token," and summon a Guardform Golem or Strikeform Golem?

AYes. The Magic Sediment would get sent to the cemetery when you pay the cost, making space on your field for either a Guardform Golem or Strikeform Golem.