These are all such wonderful hikes. Since you are not doing Whitney as a day hike, there really is no need to sleep at the Portal. If you are on the trail by 10a.m. or so, you'll be fine to make it to Trail Camp in time to set up camp, eat, relax. With your same itinerary on the mountain, I stayed at onion valley the night before, then drove down to lone pine the morning of my entry date, got my permit, and hit the trail, no problems.
The portal is really not an optimal place to sleep unless you are getting up super early to do Whitney as a day hike. It is a little high density for my taste, a bit low in altitude for acclimatization, and a bit on the noisy side, what with pesky bears and early morning hikers. It does have the Portal Store, but you can hit that up before and after your hike without staying there.
If you were open to sleeping at Hoseshoe Meadows or Onion Valley the night before, you would get better acclimatization and great access to easy-to-moderate high altitude day hikes the day before your entry. HM is all walkins, non reservable (though getting space never seems to be a problem), closer to the Portal. OV is part reservable, part walkin, maybe 30-40 minutes or so from Lone Pine.
