I see a decision in your future. To over simplify, spend a lot of money for quality stock to save time or spend a lot of time to develop quality stock. Sometimes the journey makes you appreciate the destination more.I'm just starting out so am researching into meat breeds. I would make as many pens as needed to get what I'm after.
Not sure about timeline I just started so not sure how long this sort of things takes. I'm young and fairly new to poultry and farming.
How much time would this take? Good question. A lot of times the goals change as your knowledge increases. Simple answer is as much time you think it needs.
Since you are new and this is my opinion only, set a dollar amount to spend/invest. Is this a hobby? How well do you know chickens? Get some cheap chickens and see if you enjoy it. Too many times people discover they don't like something after spending a lot of time and money. So invest the time using your budget. Spend more on the infrastructure than the livestock at first.
I knew nothing about chickens. Did some research and wanted to try it. I'm enjoying in way more than I thought I would. Start small and go from there. Ask around for a mentor. Internet is neat, but touching something is better.
Not trying to evade your questions, but only you know your answer.
Best wishes!