How many components to attach to one outlet?

You are correct that you can introduce noise back in. Generally, you would like to separate digital from other equipment. With only one outlet, I'd suggest plugging your preamp and amp into it (along with your fm tuner if you have one). Keep the digital equipment (including any video equipment like TV's or cable boxes) on other separate outlets. If you have some extra cash, you might want to research power filters for that digital equipment. Actually, that's also not a bad idea for the preamp either.

There are a number of power strips which actually audibly improve performance, acting as if they "condition" without the usual costly box. This could plug into one outlet of your dedicated line.
The one I have enjoyed is the top of the line Mapleshade Records power strip. If there is the usual oversize audiophile power plug on the end of a component power cord then three easily populate this power strip, still leaving room for more of the routine, smaller-sized power plugs of older fixed power corded components.
By necessity, in one system, I committed the audiophile sin of plugging in both analog tube amp, preamp, turntable, along with digital CDP and DAC, this visually overloaded power strip delivered excellent results, not significantly different when analog and digital plugged into different AC wall outlets. Obviously, results vary depending on the particular components, and the order of insertion of the power cords, the turning off of digital when playing records, as well as the sensibilities of the listener.
But, what audible destruction an entire computer would do to power quality on this same strip is unknown to me. Perhaps, the computer should be plugged in to a conventional isolation transformer (such as Powervar) which is itself plugged in to the remaining AC outlet of your dedicated AC line, unless you exile your computer to its own non-dedicated AC line, after auditioning the results for yourself.