When hiring your first engineers, it's important to show them you have a plan for their success at your company. The best way to do this is to have a promotion pathway laid out for different levels of engineers at your company. Aligning individual contributor goals to broader organization goals ensures mission alignment and work is focused.
You may choose to have a relatively flat structure with no titles or seniority titles. I've found this to be unhelpful in practice. It's generally good to know who's judgement to defer to when in a place of indecision. An open culture of listening to good ideas is obviously beneficial, but this should be fostered by hiring good people who don't let their ego get in the way of junior engineers bringing up novel solutions. So if you have titles, a good place to start is engineer, senior, staff, principal for ICs. You can write out the job descriptions for each of these roles focusing their responsibilities on impact. As the job description grows from one level to the next, you want the impact described to be bottom line KPIs to the business itself. Lines written, meetings run, and even launched products are not the impact you want to measure. Product landings or better yet, paying users, product uptime, and user engagement are much better indicators.
When moving up the promotion ladder, you also want to account for influence of others. ICs by definition are not managing others, but a principal engineer will have more say into more of the product than a junior eng. This comes through writing broader design docs, doing code reviews, style guides, and influencing product in meetings. This should be codified into the job descriptions, so that more junior engineers aspire to the correct things as they think about their own career progression. I've always found transparency around salaries to be attractive as an employee, though there's definitely some good arguments on both sides. Almost certainly, though, you want to be clear to each engineer the salary bands for their level and the level above theirs. Letting them be aspirational for their goals and knowing what they're working towards is important.
The most important thing here is driving company mission and focus in all materials for employees. Including their most important signal — what gets me promoted and a higher salary. This can look different for different organizations where their bottom line impact is varied. Whether they care about eyeballs for a big IPO exit, or retaining paying customers, or even social impact in a non profit. Reach out if you are looking for help aligning goals for promotion to company mission.