Using a secondary fermentation

I have a question regarding doing a secondary. I will be going to the bottling bucket as I do not have a 5 gal carboy. Let’s say I do decide to do a secondary to the bottling bucket (ale pale approx. volume is 6 gal). Will there be too much O2 in the extra volume of the ale pale (wort volume is 5 gal) to pose a potential problem on the finished beer? Also, will there be enough yeast left over from the transfer (leaving turb in primary) from the primary fermentation to have adequate carbonation in the bottle? I do plan on doing a 7 day dry hop so this will take place during secondary.

Or could I leave the wort/beer in primary an extra 7 days (dry hopping) and then transfer to the bottling bucket avoiding the turb on the bottom (add gelatin for 5 hours) then bottle?

Basically to sum this up these are my questions: if a secondary takes place has there ever been an issue with the yeast being left behind in the primary to not have enough to carbonate in the bottle? And has there ever been a problem with doing a secondary in an Ale Pale (6 gal volume) with a 5 gal wort volume?
Thanks and happy brewing!

I would just dry hop in your primary.

You definately want to minimize headspace with a secondary as you won't have active fermentation to make co2 to keep your beer from getting oxidized.

Edit:
And even after cold crashing there will still be plenty of yeast to bottle carb.

There will be plenty of yeast left to carb your beer. I wouldn't transfer this bug rather dry hop in your primary. I have dry hopped on 6 gallon buckets before on five gallon beers without problem. It will expose the beer to more oxygen which increases your chance for oxidation compared to a carboy. Again, I never had a problem doing it.

On another note, I would not use your bottling bucket as a secondary. When it comes time to bottle, you will have debris (hops and more yeast) at the bottom of the bucket which may find their way into your bottles. Even more so, it will be difficult to get good distribution of your priming sugar into your beer (as opposed to the traditional way of adding priming solution to bottling bucket and racking beer on top). This could lead to uneven carbing and potential for bottle bombs. Again, just dry hop in the primary!

Just dry hop in primary and do a good job at racking to the bottling bucket. No need to cold crash or use gelatin in the batch. Move the fermenter to the racking position 12-24 hours before hand, so that it settles back down again. If you actually gave it enough time to finish fermenting, the yeast will have already started to flocculate (or will have as much as they ever will) before then. Depending on the recipe and yeast used, this could be any amount of time from a few days to a few weeks after fermentation is complete. Dry hopping in primary is no issue (as many have found out).

As already mentioned, it's not a good idea to dry hop in the bottling bucket.

As for the trub on the bottom, that can be avoided if you rack properly. Start the siphon about half way in the finished beer, then move it lower as beer flows out. When you get low enough that you get a little of the bottom sediment too, pull back up a bit until it runs clear again.

Personally, I only move my brews to another vessel when they're going to be aging for a good amount of time on something that works best off the yeast. Such as for a few (or several) months with wood (oak, cherry, maple). Otherwise, I let it go until either it's ready, or I'm ready, to move to serving keg. Giving a brew the time it needs to become all it can be appears to be very difficult for a lot of new brewers. Once you get past that, you'll be amazed at what you get into your glass.