How much experience is required to develop an acquisition strategy plan? What training is required to be proficient at developing an acquisition strategy plan? Can an entry level person level 1 develop acquisition strategy plan?
In short, it would be a tall order for one individual to write an acquisition strategy. It takes a multi-functional IPT comprised of somewhat seasoned folks.
I would recommend that everyone on the AS team be level III certified in their perspective career fields. All certification career fields are listed in the iCatalog at http://icatalog.dau.mil/ Certainly all levels can be involved in the process, that is part of on the job training and experience to get the experience needed to become certified at higher levels. Experience is needed to make sure the key content is captured. Experience can be gained by others as they help assemble the packet.
This blog https://www.dau.mil/library/defense-atl/blog/Please-Tailor--Your-Acquisition-Strategy! Is a good read and it links to a DAU resource for Workshops. The Acquisition Strategy Workshop is WSM014, the direct link is http://icatalog.dau.mil/onlinecatalog/courses.aspx?crs_id=2108
In addition, you mentioned both acquisition strategy and acquisition plan. The terms are different and mean different things.
If you are indeed referring to an acquisition plan, then that is a contraction functional area plan. The acquisition plan talks about the contracting strategy, how many contracts, of what time, when they will be awarded, incentives etc. This is usually written by the contraction officer (contracting IPT) but would include input from a program office, as the acquisition strategy would have information needed to make these contracting decision.