Answers
Cofounders, equity, vesting and early rounds — the short answer first, then the detail.
There is no fixed percentage. A technical cofounder who joins at the start with the same commitment as the other founders usually gets an equal or near-equal share; someone joining later, part-time, or after much of the work is done usually gets less — and every founder's stake should vest.
Often, yes — if founders start together with the same commitment, an equal split avoids resentment and is a sound default. Split unequally when contributions clearly differ, such as one founder being part-time or having already built much of the company.
The standard is four years with a one-year cliff: nothing vests in the first 12 months, 25% vests at the cliff, and the rest vests monthly over the next 36 months. It's what most investors expect and what most founder agreements use.
Both let investors fund you now and receive shares at the next priced round. A SAFE is simpler because it isn't debt — no interest and no maturity date — while a convertible note is a loan that accrues interest and comes due, which gives investors a little more leverage.
Pre-seed is usually the first outside money, often raised before real traction to build the product and find early customers. Seed typically follows early traction and funds the search for product–market fit; the exact boundary varies by market and year.
Check three things before committing: that you can actually work together (do a small, time-boxed project), that your expectations line up (commitment, equity, ambition), and that their track record matches what they say (references and past work).
No — solo founders do build and fund successful companies. But a cofounder with complementary skills shares the workload and risk, and many early-stage investors prefer backing a team.