The ULN2003A should work fine as long as you keep power dissipation in mind - Darlington transistors will saturate at a bit over a volt, just calulate out how much power will be dissipated when the max number of solenoids is activated. If you need higher power capability, a number of companies make Mosfet based parts that have a lower on-voltage.
As for the sensors, the OMRON part seems to be an open collector, so you can just use a pullup resistor (~1K or so) to 5V, and it'll never exceed the logic power supply.
As for the Proximity sensor, I can't get to the datasheet (blinkin plugin...), so I don't know... If it's also open-collector, you can do the same, otherwise just have a single transistor buffer, setup as an inverting common emitter amplifier. You might be able to get away with a ~10K resistor connected directly to the IO line to limit the current to a few milliamps, but a single transistor never hurt.
One question though is isolation - This sounds like it might be for an industrial type app - in which case you might want to use optocouplers for everything. How long are the connections / what's the environment this is going to be used in? How much would it cost if something blows up from ESD/ground loops...
James