You need licensed contractors and permits for electrical, plumbing and for major things, someone who knows how to put a roof on and address foundation issues.

My best recommendation here is to get with other investors in your market and ask them what techniques and companies they are using for foundation work.  

I think this would get me a good foundation to be able to then figure out what I would have to charge later on and give the experience to make the best choices when fixing up the duplex that I purchase.

@Michael MorenoYour proactive approach to building equity in your first property is a solid foundation for an exciting real estate investment career.

Other start-up costs such as appliances, which are normally considered capital improvements, become deductible in the current year under the de minimis safe harbor provision of the tax code.Note that some renovation costs will always be considered capital improvements regardless of whether or not a property has already been placed in service (for example, replacing the entire roof).Examples of renovation items you want to complete before you place the property in service:fixing structural issues (for example, cracks in the foundation)replacing an entire roof, floor, bathroom, kitchen, or plumbing systemadding a deck or new HVAC systemExamples of renovation items you want to do after you place the property in service include:painting installing appliances replacing a doorknob or windowrepairing an existing plumbing systemother minor repairs

And to purchase, lay the foundation, electrical, install, and get permitted, I typically have my clients assume $10k total. 

it's your foundation, not your end state.

But a SLAB foundation.. whats your thoughts on that vs a basement / Crawlspace setup for a duplex rental?

But to summarize these requirements think big ticket items, roof, electrical, and foundation.

There is not a persistent issue under the slab, but very infrequently there can be which has been a grading and neighbor directing water toward the foundation issue.