After buying and selling multiple pieces of real estate, we still own a house hack (somewhat unconventional approach with a carriage house & primary home), but we love the flexibility it affords us. 

From what I’ve read recently in the Wall Street Journal, some lenders have been more flexible with assumptions.

If you're growing your portfolio quickly, the added flexibility can make it worthwhile.

I am wrapping up my licensing education with the intent of being able to buy and wholesale solo part-time, while keeping my full time job.How would I go about finding a brokerage that would sponsor me as a sales agent while allowing me to have this flexibility?

Thats just not an option.....Care to put some $ on that bet? 

The licensing costs are minimal can offer flexibility to your buyers.  

This gives you more flexibility and protection in uncertain economic times.Scaling: Once your investment is stabilized and your systems are running smoothly, start planning to scale.

Be flexible, adjust to the times, and use financing judiciously to advance your investment goals.David KrulacBigger Pockets Podcast #82 

I think that overall, multi-unit buildings will be your best bet if you don't want to risk getting in trouble with condo associations. 

Your best bet at that size is not going to be mezz, most of them cut checks at 2mil minimum.