Beginner priority: after raising Keep level, upgrade Academy and Rally Spot first — Academy research raises many buffs, Rally Spot increases march size for gathering/combat. Construction speed boosted by: Academy Construction/Adv Construction/Super Construction research plus Typography/Super Typography to speed that research; Strength Crown gear before starting; Duty Officer at the Keep before starting (ideal Menshikov or Zhuge Liang, +20% base skill); Alliance Science; also Civilization Treasure (Mask of Agamemnon), Victory Column, Dragon (Celtic Demon). Buildings that disable core function during their OWN upgrade: Hospital (no healing, SvS revive ok), Shrine (no general revive), Walls (no fire-extinguish/repair until done, then full recovery), Academy & Military Academy (no research), Forge (no crafting, but Dragon->Ares upgrade at Lv30 still works), Stables/Archer Camp/Barracks/Workshop (no troop training), Research Factory (no research-stone production), Bunker (no troop deposit). Consuming Return Event matters most at Keep level 25+.
Original research source: Evony Guide Wiki