Keyboard and Mouse alternatives
I asked about available choices at a nearby Apple Store. I prefer the wired keyboard, since it has the numeric keypad attached and important (to me, at least) keys for PG UP, PG DN, etc.
Any mouse is OK. To Apple, the wireless keyboard (smaller) and wireless mouse are standard. But you can get any keyboard or mouse at no extra charge.
There might be small charge to get a trackpad. My wife is dedicated MBP user, so she prefers a trackpad. I would assume other laptop users would have similar tastes.
When you have a wired keyboard or mouse, you might have more clutter. But you never have to change a battery, either.
I'm not sure if Apple retailers have the same no-charge options. I do know that you will never be able to get Fusion Drive in an iMac bought from Amazon or Best Buy.