Yes what Gary said would be best for you personally. If you do not plan on submitting a lot of cards it wouldn’t be worth getting the psa subscription. Unless you have several cards valued higher you want to use the free grading voucher for.
Do you know if there is a price limit on the cards that you can use on the E4 service? I have a couple gold stars that I want to grade and on the psa site it says bulk price should be under 100 each?