Most issues regarding phase come from the recording world.
https://www.soundonsound.com/sos/apr08/articles/phasedemystified.htm Lots of articles regarding phase can be found on sound on sound. You don't have to worry too much about it (you're not going to have any bleed from the samples you're using). Really layering will be one of the biggest issues. Collapsing your mixes to mono while mixing will help avoid deconstructive interference, but its only a worry if your music is going to be played through a mono system.
When you talk about linear phase, it usually applies to EQs. You'll have to check that out online, I can't explain it that well.
Hearing if things are in and out of phase is day and night. Had a recording session last night, when we phase flop one mic (puts it 180 degrees out of phase), we got a tonne of cancellation. This means our original (pre phase flop) signal was almost close to being perfectly in phase. Adjusting the phase of a sound is done differently in software than irl. To adjust the phase of a signal in real life, you literally move a microphone farther or closer. Synths you can set the start point of the wave you have selected. When you zoom close in to a waveform in your daw, you can see the positive and negative excursions (similar to a sine wave going to its positive and negative values). Shifting that in relationship to another waveform would also be adjusting the phase. Again, not much to worry about since you won't have any bleed from other mics (samples are clean!)
I hope this wasnt too much of a mess and answered some questions. Check out sound on sound for phase and all its meanings. Lot's to learn.
