They instead focus on fully gutting their projects and install entirely new kitchens, bathrooms, fireplaces, accent walls, etc. and any exterior or mechanical upgrades necessary.While I understand this whole hog strategy, part of me says this will end up increasing the value of a home so far beyond other homes in the surrounding area that it wouldn't sell for what it's likely worth.

the buzzword  is diversification - but with the purchases I made at the time - real estate far outperformed the stock market.  

I'd like to be able to use my phone to measure the space digitally and then work on my laptop to create a design, especially for things like a kitchen with different options for cabinet placement, etc. 

If you use a properly vetted, reputable and experienced GC, statistically it seems less likely there will be issues compared to a fact pattern where  you self manage  the work as a first timer.

Can they use the kitchen or would you prefer them not?

Especially when it comes to bathrooms and kitchen.

Infact, it's advertised online with the Realtor.com site showing all the amenities of my apartment, the electrical, the plumbing, the windows, the door, the shower and toilet and even the kitchen sink so obviously it must be legal because I can't see an agent of his caliper risking his career and livelyhood for undisclosed info.

I went to see some tiny homes here in Pomona California. 20x20 foldable container house two bedroom one bath kitchen living area for $28,000.

So I basically would want a person who looks at the whole house and gives me the appraisal cost, the areas that need fixing (ex. kitchen cabinets, tiles, bathrooms, plumbing, electricity, etc.), and how much the cost would be.Then this way, I could decide to proceed or not based on the assessment.

Fresh landscaping, new paint, new layout, add a bath, a room, a garage, finish the basement, new roof, kitchen etc are just some ways to add 20,30,40K to the value with sometimes minimal investment.