We'd like to ultimately move into a larger single family home and rent our current condo.We bought a 2 bedroom condo in 2014 for $160k (15yr mortgage) and have now outgrown it.

Can I use my potential income with the STR to get approved for a larger mortgage on the duplex?

We were due for our first child in June and figured we might as well just complete the purchase since we needed a larger space (we were renting a 600 SQ ft basement suite from our friends mom and dad) and we figured the rental in this future home would help hedge any risk with making payments in the future.The property was listed for $275k, we offered $280k and asked for new electrical panel and all closing costs to be covered by the sellers after inspection.

lol.If you're concerned about neighboring properties, you need a much larger piece of acreage to build on so you can create some buffer zones in all directions.

Alternatively, look at the square footage of your property and compare to those that are larger to see if there is a big jump once you pass a square footage threshold.  

If you really wanted to, in theory the money you would have put towards renovations could now be used towards a larger down payment or even buying the next property.3.

Otherwise, they pay a larger utility fee each month and they share the basement utility room (laundry, storage, and bikes). 

I have been licensed since 1975  I have wholesaled I cant tell you how many properties well over 1000 that's for sure.But you have to define wholesalingMy definition is I buy them close on them  then usually do something to improve them sometimes not and then I resell them.If your definition of wholesaling is to simply make larger fee's than a normal brokerage commission ..

Seems like a HELOC on both would be a good choice, but I'm concerned about getting over-leveraged.Any other thoughts or ideas about our situation and early research that could help us out?

Fairly far away from other larger centres.