Need advice on adding a line and upgrade

I have an experience more account with 4 lines. 3rd line is free and I also have a friend discount. We’d like to add a 5th line. I’d like to upgrade my line (14 pro) to the 18 pro but that’s not urgent. We also have an unused 15 for trade-in but would probably use it on the new line. I was thinking the Costco route to maximize savings/gift cards. A few months ago, Costco recommended the line bogo and get 2 galaxy 26 for free. And then the extra line would just go unused or maybe for a side business. What advice do you have? Here are our account details. Lines 1 and 2 are $112 with ported over (and upgrade eligible) iPhone 14 Pro and iPhone 15 pro. Lines 3 and 4 are iPhone 15s on installment for $4.16 each. Line charges are $24 combines because 3rd line free, autopay, and friend discount. Taxes are another $26.63 for a total bill of $170.95.