Guild GP is not very relevant to the calculation anymore. Guild preparedness and organization is much more important. The number of RJT squads you have likely significantly impacts your T6 speed - but you don't need as many for heroic as in the past.
You should aim for:
Phase 1 - ~15-20 decent RJT squads.
Phase 2 - Hard to calculate: Everyone should have several viable squads. Examples include: Ackbar/Leia spam, Nute/Leia squad, Wampa team (GK or Fett lead), Jedi (GK or Bastila). A solid Revan team can now do 10-20% of phase 2 and drastically reduce your guild's requirements
Phase 3 - ~30 Chex Mix teams. If you have players who are consistent at the Talzin lead Nightsister "Death Storm" squad in phase 6, you can try to use them here, but it's very RNG dependent.
Phase 4 - ~5-10 decent zVentress Nightsister squads.
Check out the Discord server "HSTR Project" for handy resources, squad building tips, and an entire community built around helping new guilds reach Heroic level.