Can I order a SIM and activate it after a few weeks?

Golnaz your Sim card is always ok. You can choose to activate it later. Not the last day for your transfer just in case;)
No credit checked but you need to have a credit card on your account but you can have a prepaid card.
You can use a Visa or Mastercard credit card (including prepaid), or a Visa Debit card to pay for your Fizz plans.
Other cards such as debit cards, American Express (Amex), Dinners, and others are not accepted. Foreign credit/debit cards are also not accepted. You also cannot use the funds from your Fizz Wallet to pay for your monthly plan.