It's encouraging that the secondary school Senco has agreed to meet with you beforehand. Many don't (partly due to workload).
You will know what your Ds's triggers/difficulties are but a few things to cover, I would suggest:
Is the school running any additional transition sessions/days?
Are you able to meet with/talk to your DS's form tutor before he starts? Or how can you contact them if any difficulties arise? If there any friendship issues you need to cover off from primary? (If others from his primary are attending the same secondary.)
What will homework look like for Yr7s. If you feel this may be an issue you can flag it now. See if the school run homework clubs. (Some DC with autism refuse to do homework at home, or feel overwhelmed by the expectations.) Schools should tailor their homework expectations for DC with additional needs.
Likewise with PE. Some DC find changing difficult, need extra time, support to participate. It's worth flagging up if competitive team games are an issue.
Will your DS be OK with the uniform? Some DC have sensory issues around ties etc.
Is there somewhere for DC to go at break/lunchtimes if your DS feels overwhelmed. In my experience, it's the unstructured times of the day that can be the hardest. Some DC go to the library so it's worth asking if that might be possible. Are there clubs someone could support him to attend?
How does the school support DC to make friends?
What does lunchtime look like? Will your DS be able to cope with the queues, the choosing?
Do you feel your DS needs extra support around his learning? You don't say what his academic profile is like. Many schools run 'nurture' groups in key subjects like maths and english. So it's worth asking what they look like.
Support should be based on need not diagnosis. However, as I'm sure you know, schools are really struggling with decades of chronic underfunding. If your DS's support needs are significant, it may be worth applying for an EHCP as without one tailored support can't be guaranteed.