Oahu, Small house renovation. Coverting room into bedroom/bath

[Andrew Cannon]

Do contractors on Oahu typically need professional plans drawn for small house renovation jobs?

Can I draw my own plans on sketch-up even though I have no planning certifications in order to submit for city permitting?

Anyone familiar with permit timelines for converting rooms into bedrooms and bathrooms?

Back story:

I currently have an accepted offer on a project in Waialua. My plan is rehab, live in it, then flip in about a year or so when I move back to the mainland for work. I have already had a contractor look at it and he suggested getting a professional planner to draw plans of the rehab. The house will need a room/hallway converted into a bedroom, bathroom, and wet bar. This would turn it from a 2bed/2bath into a 3bed/3bath with potential for split rental income for future owner. The plans, I’ve been told, should pay itself back with streamlining permit applications as well as creating clearity of job scope. The house will also need some modernization throughout with focus on the kitchen and bathrooms. All this I’m looking to keep on a modest budget and am willing to do as much of the work myself if needed. I’m most likely going to work with the contractor I have already established a relationship with but am open to get competitive bids. 

Thanks for your time!