For the ASG question - IF they are one - there is a whole other issue of not having a SIMPLE at the same time as a 401(k) plan, by the same employer. And an ASG is treated as a single employer for those purposes, so generally cannot have both in the same year. Determining the status of the SIMPLE would be very important.
The deferral limits for short initial year 401(k) plans generally aren't pro-rated as they are personal limits, not plan limits, but the plan document should address if there is any pro-ration of limits (deferral or otherwise) for an initial short plan year where there is no prior SIMPLE or predecessor plan. If there is a basic plan document for the 401(k) plan, you should read it carefully.