I have comps pulled, and my next step is to get a contractor/estimator out here to give me a better idea of rehab costs.

That's how I would estimate it.

I am getting another roofer company to come out next week to give estimate on yearly inspection/maintenance. 

Many have been burned by relying on their estimates.

Plus most hard money lenders will require a fair market appraisal.If you plan to rent, you already have that documentation plus the appraisal will provide estimated rents.

I'm trying to buy my first investment property with ~$100k saved up.My brother started his first W2 job last month that pays $45k/yr+ commissions.I plan to get a minimum wage job/an entry W2 job since I'm still in college and to hopefully qualify for a bigger loan.A lender estimated we'd be eligible for a $300k loan with $100k down, and a $2,500/mo payment on a $400k property with only my brother's income as of now.California is too expensive for us so I have been looking into out-of-state investment properties.What would be the best investing route for us to take to grow our wealth?

So I take what you have and what you expect, estimate the time it would take in a whole year of work and create my flat rate.I notice short term rentals are about 1 hour a month of work per property, since we need to track each property's Profit & Loss for Tax time, this is also tracking a mortgage and depreciation as well for that property.

@Lauren SanfordI barely learned I could resell and estimated around 50k at 0%.

Stock market returns estimated to be much lower next 10 years.

Just get lots of estimates, as they can differ by thousands.