Yes, keep all time you need. Also while you are updating this level pack, probably the official SRB2 is getting an update, so you could wait also for more stuff, and when you get more new things to add you could probably update the level pack adding new textures, gimmnicks, lenght and gameplay. Probably you though this, i remind you said me you will use only the official bosses.
For unlockables and emerald hunt in v 6.0:
what can we expect? (A Super Sonic level, a new level, mini games, shortcuts, archives or another type of easter egg?)