Can you add multiple referrals on Public Mobile and plan question?

I'm on the verge of signing up for Public Mobile. I have a question, can you add multiple referral codes so we can save money? How would I do that? (Obviously, some of you may post referral codes soon.) I have at least one referral lined up. (Family member)

I also signed up for the 2 GB bonus promo. Which plan should I get, the $33 5 GB, or the $38 7 GB? (Including the promo and auto pay discount.) My max budget is $40 for a plan.

My current plan is the one in the signature below. (Lucky Mobile) Do you think it's worth signing up for a better plan? (I went over my plan, and had to live with 2G speeds.)