The key limitations in your situation are those at DFARS 217.204(e)(i). Specifically, the base contract cannot exceed 5 years and subsequent option periods cannot result in greater than a 10-year total ordering period. One limitation to this DFARS flexibility at paragraph e(ii) applies to Advisory and Assistance Service. It's up to the contracting officer to determine any of the labor categories mentioned in your question are covered by the definition of A&AS in FAR part 2. If no other prohibitions at DFARS 217.204(e)(ii) apply, I see no reason you can't award a five-year base period with one five-year option period. I'm unaware of any specific authority your organization may have for a base period longer than five years, as FAR 17.103 specifies a five-year maximum for multi-year contracts (there are limited exceptions).