In my experience, when we lived in the city and kept chickens, they did eat my plants in the garden when they free ranged. They dug up all my plants close to the house and made a mess of the mulch. When we kept them in their own space with a stationary coop...they go super stinky.
I would go with a small chicken tractor. We have one now and we just pull it forward every day and there is virually no smell and the chickens are safe from predators and our garden is safe from the chickens and my decorative plants are safe from the chickens. The chickens still get bugs and fresh grass every day.
As far as just keeping two egg layers, I don't think that would be enough. Chickens skip laying one day a week so, there would be one day when you only get one egg or no eggs...we eat eggs every day for breakfast so we atleast need as many chickens as per person and if you bake at all you need extra eggs to do that. I would say 3-4 chickens would be a nice size flock and if you get over run with eggs, you can make egg noodles or pudding or something that uses them up.
Depending on where you get chickens, if you mail order you have to order a batch of 25 usually. Is there anyone you could split your order with? Can you just pick up 10 birds at your local tractor supply store in the spring? Keeping a small flock of chickens is not cheaper than just buying eggs, even super free range organic eggs..because you are buying so little feed you cannot get a discount...so only do it if it is a hobby you want...not cost effective in my opinion.