Create entry in mulitple collections on user sign up

My product enables customers to answer a series of prompts. After all their prompts are completed they can then print a book based on their answers.

Taking each piece of data needed for this process into consideration, we have over 300 data fields we need to track for each user (this includes things like image uploads, answered question counts etc.)

Question 1: Is 300-400 columns in a collection too much? Will it slow performance? (My target is to get > 1000 users in the first 3 months, then target 1000 new users/mo.

Question 2 (real question): I thought that it might be so I decided to split the prompts across 4 different sections. The collection setup is read/write based on logged-in user being the original creator. When a user creates a profile, is there a way I can trigger an entry for each of these 4 collections so that they can jump in and begin working on anyone of them at any time?