Newbie zoning / subdivision question

[Yinan Q.]

I have looking at a house on a large piece of land that I am thinking to sub-divide and build new homes on. I researched on this topic on BP for a while and there are a few questions I couldn't find answers for. 

So the land is about 1.2 ac and zoned R-4. The land is adjacent to lands zoned R-6 and R-8 on three sides. The existing house takes about 1/3 of the land to meet the setback requirements. Here are my questions:

• Since it's zoned R-4, theoretically I can subdivide the lot and build 3 three houses. Do the new lots have to be relatively equally sized or they can be any sizes as long as the setbacks and land coverage ratios are satisfied.
• When calculating the land coverage ratio, is road and public area (walkways, playground, etc.) included? Or it's strictly the lot the house sit on?
• How difficult (or easy) it is to get it re-zoned? Since this particular lot is next to R-6 and R-8 zoning, maybe it makes re-zoning a little easier?

I am planning to talk to the City's planning department and I want to be as prepared as possible. Any advice you can give will be appreciated.