Special Summoning After the Seal of Orichalcos
My question is this, after you activate the seal can you Special summon monsters from other places?


Yes. The card is being explicit by stating that you can't special summon "from your extra deck".

You are free to Special summon from other places (hand, deck, graveyard, banish).


  However once the card has been out on the field can you Special summon again or is the effect continuous and would destroy any addition Special summoned monster?


Once the card leaves the field all of it's effects stop working. It is a continuous effect, but precisely because of that is that it's effects only last while face up on the field. From the wiki on Continuous effects we have, emphasis mine:


  Continuous Effects (Japanese: 永続効果 Eizoku Kōka) are a type of monster effect that applies while the monster [or card] remains face-up on the field.