You can plug your guitar into your effects unit and plug that unit (pedal or board) into the Left "line in" 1/4 inch input - in either channel two or channel three. The left input is for a mono signal.
You can plug the stereo output from the electronic drum module into the left and right input of whichever stereo input channel you did not use for the guitar effects unit. This would leave channel one open for another line input or a microphone.
You can connect the headphone amplifier to the headphone output labeled "phone" on the mixer using a 1/4 inch TRS to 1/4 inch TRS stereo patch cable.
You can input a signal from your phone or other source into the left/right RCA jack input on the mixer. You can also output a signal from the RCA out jacks. If inputting from your phone or other mp3 device that has a 1/8 inch headphone jack, you will need a 1/8" TRS to dual RCA cable.
If you start playing for an audience in the future - you can send the entire mix into external powered PA speakers or into an external power amp (to drive passive PA speakers) from the L and R main out jacks on the mixer.
As far as your question about if that would sound as good as a jam hub through your headphones - I have no way to know the answer to that question without trying them both side by side. You can look at expense and future potential use of each system as a deciding factor if you are not able to do your own test.
If I had to guess, I would say that either the JamHub or the mixer with headphone amp would allow you and your jam mates to hear everything you need to hear and control the volume in each headphone and practice together without external amplification. So I believe either system will accomplish your goal.
Whichever system you choose - have fun jammin!