in that you seem to be sizing the mission based on an arbitrary number of Proton launches rather than sizing the number of launches by the mission requirements.

My perferred approach is to begin the planning at the end of the mission and then work forwards to the launch.

1. What will be required to either slow the vehicle into Earth orbit or return the crew directly to the ground? Will you use aerocapture (as yet untried) or thrusters to enter Earth orbit? If you're going for a direct atmospheric reentry Apollo-style, what form of heat shielding and landing equipment will be necessary? This is one of the tougher requirements to meet. Use this as your baseline mass.

2. What will be required (propellants and consumables) to fly the mission from the NEO back to the Earth? It takes a finite amount of food, oxygen, water, etc. per crewmember per day to survive. Recycling can reduce this somewhat but not completely, and recycling equipment has both mass and cost. Add this mass to the baseline.

3. What will be required to support the mission while on station at the NEO? Add this mass to the value from #2.

4. What will be required to support to fly the mission from the Earth to the NEO? Add this mass to the value from #3.

5. Your baseline habitation module will need to provide everything the crew needs to survive for a period of several months to perhaps a bit over a year. You'll need some living space, exercise area, electrical supply (solar panels and batteries), food, water, communication and navigation equipment, etc. Your module will need extra radiation shielding because you're beyond the protection of the van Allen belts and you need to think about protecting the crew from things like solar flares. If you're going to recycle, you'll need that equipment, too. For a mission of this length, it might not be worth the trouble to recycle if you're talking about a small crew, say 2 people. Something along the lines of the Transhab proposal could be well suited for the job.

6. How much propellant will be required to accelerate the mass from #5 to escape velocity?

Since the mission will take several months, you'll probably need storable hypergolic propellants. Once you've calculated the masses at the different stages of the mission, you can determine how much propellant will be required for that stage. Once you've figured out all of this, then you can estimate how many Proton launch equivalents it'd take to fly the mission. Just guessing, I suspect it'd take more than 2 Proton missions worth of propellants to fly an NEO mission but it all depends on the underlying assumptions. Then, you have to be able to justify the cost of doing this as opposed to sending several robot spacecraft for the same price. I think it would be a cool mission but perhaps more expensive than you're thinking.

I know of some satellite systems that cost a billion dollars each, so I have a hard time believing we could send humans to an NEO for $1-2 billion. If we let the Russians build and launch the mission, it'd cost a lot less than doing the work here but then we have to figure out who is going to pay for it.