1. I like to start at Alpha due to easy accesses to the mountain area for fast Mithril, Adamantine and Manganese runs and good premade cave in the biodome for starting a machinerooms and mines. Only downsite being that you don't have a good water source closer than the swamp (atleast I think so).
2. For diamond level material I usually just use the obsidian I get from the jungle village blacksmith because turning that to pickaxe head doesn't need the smeltery XD.
3. Tbh I have actually never had the need to expand any of the biodomes.
4. At the start I usually use meat and apples and after i have gathered around 160-200rep I start to mass request emergency nutrition bars.
5. Most of the time I go for Oureclase/Mithril armor and at some point upgrade to Adamantine, Tartarite or mix of those 2 and Thaumcraft armor.
And for weapons I use Adamantine/Enderium/Damascus Steel rapiers and random bows.