I’m reclass to 35L from 11B or at least I want to. Do 35L get promoted to E5 after ait? Can somebody explain that to me?

Yes it's called SMAPP, you promote once BLC complete. But you should have no issues promoting as an 11B

According to some sites I've seen, yes you have to be a SPC at a minimum. And, according to MILPER Message 12-023, Soldiers are promoted to SGT upon completion. However, you really should talk with your Career Counselor to get up to date information

In my case, when I started the process to reclassify as a 35L, one of the things I was told (and you can read in the CI recruiting page) is that you need to be E4 or E3 and that E5 will not be accepted, already in CISAC, several of my colleagues (Active Duty) were E5, some were promoted after being selected, and another told me that he applied to CI being E5, and that (apparently) there is a waiver for that in OCMI. Regarding the promotion under SMAPP, I don't want to go into details that I don't handle since I am not an HR specialist, but before going to CISAC I received a decision report and a SMAPP memo, and the decision report explicitly stated that the effective date of promotion to E5 was CISAC graduation day. I personally received my promotion by normal channel and not by this SMAPP method, but other specialists who were with me at CISAC (we keep in touch in the group chat) have told me about their experience, and they were promoted without going to BLC, with the decision report, SMAPP memo and MOS orders (you brigade have to request it upon graduation from CISAC, in my case I received my 1059s and a graduation certificate), but they were automatically promoted to E5 with those documents submitted by the S1 to HRC. It is worth clarifying that none of them are BLC graduates, but they were asked for the DLC 1 graduation certificate. Again, I am not a specialist in human resources, and I share with you the experience of some of my classmates, maybe the new unit will send them to BLC in 1 year, maybe not .... the truth I do not know, but that is the armed forces in general, nothing is 100%, you go from one installation to another, and it is a different army. Best of luck and 35L is a great career to follow.