Are there any good guides out there for designing/Bricklinking your first custom?

I am considering building a custom TIE Fighter heavily based off the TFA mode - I'm thinking base frame + wing joint to keep things simple for myself, with colours heavily swapped out for shades of red. Looking for tips around:
* Going from ideation to LDD
* LDD to Bricklinking
* How to choose from Bricklink sellers etc. Maybe general weights/cost tables or calculator for different countries & perhaps delivery times (to save time researching into each country's national post website).
* Maybe a rule of the thumb number of spares as a % so the design is not royally screwed by a few missing critical pieces (I don't have disassembled sets to salvage from, so this project is do or die).
* Anything else a noob should be aware of?

Thanks in advance guys.