You can do it probably, but you need funds to get the materials first. Dont expect people to pay upfront for you when you are not know and when they know you just buy parts and assemble them.
Are you also ready to take the tool if parts don't work together? What if the Neck is fucked or it needs proper refret job or leveling at least, are you paying another 150-200 euros for it (being nice) and then add it to the customer, why should he pay extra for it?
Can you get nice deals on ordering 200 pickups (or tuners, bridges, etc) at a a time from a known Brand so you can get a nice discount? Ok so you want to use less known brands... that will cheapen the guitar, doesn't matter if they are amazing or not, people pay for brands not for "unknown" quality.
If you want to do it start very very slow, do one for a friend, see how long it takes you, keep doing it if it compensates, you will loose at least 1-2 weeks on each initially do you think you can make the money to cover that time?
Last but not least, as Business you need to pay taxes and buy tools and take care of the publicity of it.
Wish you luck nevertheless