After removing old carpet on stairs, I found the treads were bare 2x10 pine (or spruce?) and risers are bare MDF. There is 1/8" gap between the risers and treads. Due to limited budget, I decided to paint the stairs and refinish the oak handrails/spindles. Here is my plan:

1. Fill nail holes and sand treads.
2. Sand handrails to remove existing polyurethane
3. Apply primer. Then paint treads and handrails with dark chocolate latex paint. 2 paints I'm considering are : http://www.sherwin-williams.com/painting-contractors/products/catalog/porch-floor-enamel/

or http://www.benjaminmoore.com/en-ca/for-your-home/paint-products/benjamin-moore-flooring-solutions#piSheen=112&advs=0amp;tab=2

4. Apply 3 coats of satin polyurethene for extra protection. sand lightly between the coats.
5. Cover risers with 1/4" plywood paint with white Sherwin Williams trim paint - ProClassic Interior Acrylic Latex Enamel. I have some leftovers when I did the baseboards a while ago. It's great product.
6. Sand spindles to remove existing polyurethene
7. Paint spindles with white Sherwin Williams ProClassic Interior Acrylic Latex Enamel

Is the plan feasible? without too much experience with stairs and handrails, I'm a little bit nervous. My questions are:

1. How to remove existing polyurethane efficiently? Shall I remove the handrails and spindles for this?
2. Did I select the right paint?
3. Can I apply polyurethane on top of latex?

many thanks.