Is there a time frame which you need to port in within a few months?
You will be using 2 lines (Eight and CL) right?
For Circles Life promo code that does not includes the "$0 New Number fee" add-on, you need to port in to Circles Life within 30 days to be eligible for the $10 Lifelong Port-in discount.
Newer promo code that include "$0 New Number fee" doesn't allow the $10 Lifelong Port-in discount to be stacked.
Using this promo code as an example: PRT1TB650CAIU5YFO2G
You are not eligible for the $10 Lifelong Port in discount. So don't need to rush to port in.
If you are using the "SUPER38" promo code, you need to port in within 30 days to get the $10 Lifelong Port in discount.
For your 2nd question, yes will have 2 number during the interim period (Eight + CL). Since Eight Mobile is free for 88 days, it won't cost extra expenses to delay the extra number.
Since Eight Mobile is offering the 88 Days Free Day Service if you sign up and Port-in by 28 Dec 2025, you can sign up a new number with CL, upon receiving the new CL sim, schedule a port-in about 80 days later. You should give a buffer of about 1 week when porting your number just in case it takes slightly a longer time.
If you do not want to hold 2 numbers during the long interim period, only sign up for a new CL number about 80 days later, but the risk is that the CL promo may get expired.