Secondly, should Building LLC be separate from Wholesaling LLC(currently being used for wholesaling).

Separate LLC per Property: Maximizes liability protection but adds complexity and costs with individual tax filings.3.

Quote from @David Contreras: How difficult is dividing land that used to be separate, but is now a large lot as a result of a voluntary merger by the previous owner ? 

As a general rule, each entity that files a separate tax return (partnership, s-corp, c-corp, etc) will need its own QBO subscription.

You may want to get a GoogleVoice number to separate from your personal number.

HI Henry,You would want to make sure your county allows you to condomize it so that you can two separate parcel numbers for the main house and the newly built DADU/ADU so that you can get appraised separately.

Find the ones that can do it, and it also helps if you have separate contracts for the lease and the option. 

Also if the house needs rehab, how are you going to fund that.Is it deeded separately?   

Are there separate mechanicals for each unit?

Using a lower-cost skip tracing service and then a call/mail/sms campaign service separately may reduce your costs.