If you can get financial support to get a duplex/triplex, I would recommend this.

@Serge Hounkponou Recommend you first figure out the property Class you want to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

Starting with local credit unions is a good idea.2 - I recommend starting your search with a Realtor who specializes in working with investors.

I see you're in the Boston area, so if you're looking for cash flowing markets I'd recommend Lowell, Fitchburg, Leominster, just to name a few.

For flipping I would also normally not recommend adding an ADU.

Which sites do you recommend for pricing? 

I can definitely provide a recommendation.

Pick a screening platform/application that makes sense for you.As for meeting the applicants, I recommend meeting them at the property to show the place to them rather than getting coffee or food with them.

I recommend having a pricing software (pricelabs perhaps). 

I'm a little biased (am the owner) but seriously pumped to see you recommending it.