I pushed back on this and requested a re-appraisal - I submitted comps showing what other less desirable condos in my area have recently sold for - but the appraiser is sticking to his estimate (of course he's not going to admit he made a mistake).

It sounds like you’re off to a great start, and I totally get where you’re coming from when deciding between an online bank or sticking with a local one.

Best advice:  Keep strict screening requirements and stick to them.  

Tighten up your policies and procedures and stick to them.

Additionally, would it be better to specialize in one area early on and stick with it post-graduation, or should I explore different sectors before committing to a specific path?

Depending on the construction of the building (block or stick, etc), you will want to test the connection strength.  

;-) My GC in colorado has had his subs stick with him for 10+ years and has a stellar reputation for under budg/under timeline rehabs... 

This is very important so see if you can stick with me here.A motivated seller is not someone that want to, needs to, or even has to sell their house (like foreclosure, tax liens, job loss etc. etc.).A motivated seller is anyone willing to sell their house below market value regardless of the reason why.So it is the willingness to sell below market value is what separates a seller from a motivated seller.Take someone in foreclosure.

Pick your niche and stick to it.

I won't go with the riskiest opportunistic strategies, and will stick to core and core plus mostly with some value-added.