As a contractor I can tell you that most reputable contractors probably don't need your job, and if you make things too complicated or troublesome, they will move on to other jobs that don't throw up red flags. Much of what you ask for here is reasonable, but bringing a second contract into the equation can set of some alarms that you may be a difficult customer to work with or even a litigiously minded person who is likely to try and bring a lawsuit whether deserved or not. Anything you want covered should be in the original contract.
There are a wide range of costs associated with remodeling a bathroom, including size, the type of materials, its current condition, and the location. Homeonwers spend on average between $15,000 and $25,000 in their bathroom renovation. For example, the average cost of a 100 square foot master bathroom with tile walls and flooring, new fixtures, double vanity, and walk in shower with separate tub is around $20,000.
It's so competitive out there. I am a Long Island contractor and I be realized lately that clients give you an impression when you give them there costs that you are doing something wrong. I've been in this Busines about 20 years and that avg cost is right there. Also homeowners should also realize if us contractors are using subs for our plumbing and electrical our costs are hire than the guy doing all the work himself. I only used licensed contractors for all my remodeling work.
It's totally legitimate for a professional to charge you for a design, at least in some situations. If the contractor has a book of ready-made designs and just pulled one out to show you, then you're right that s/he shouldn't charge you. But if someone does a design that conforms to your room's dimensions, with the features that you want, then that person has invested time in creating a work product. Some contractors and architects think that's just the cost of doing business, but many others consider that their time is worth something, and they charge for it. You just need to let contractors know that you're not looking for that kind of custom work, and not willing to pay for it.
I acted as general contractor and did all my own demo to remodel my 6x8 bathroom. I hired subs individually to do most of the work - an electrician, a plumber, a drywall guy and a tile guy. I painted the walls and the ceiling. I replaced everything except the cast iron tub. Materials and fixtures cost around $2000 and labor was about $3000. My subs had no problem with me supplying the materials, because I discussed their job scope in advance. This project took 6 months but I did have another full bath to use in the mean time.