The bottom-up method has not yet had time to make such large structures. This is best accomplished if you start with smaller scale clumps. The best reason is observational evidence. The shocks produced by the collisions will induce star formation, using up the available gas in the spirals, and the stars, which originally were in disks of 2 different orientations, will wind up in orbits of arbitrary orientation. This is what an elliptical galaxy looks like.
Minor mergers induce star formation in the larger galaxy, and usually canibalize the smaller galaxy.
If the orientation is right, this can produce a ring galaxy from the induced star formation. However, the larger galaxy remains a spiral and the disk remains intact. You are required to answer either question 2 or question 3. Extra credit will be given if you choose to do both, and I urge you to at least give a second problem a try. Observations show that objects in the Milky Way galaxy, and in many other spiral galaxies, revolve about the galactic center at the same velocities, regardless of distance from the center, beyond about 20,000 light years from the center.