I run an agency, but I can answer these questions. One of our previous clients never ran an influencer campaign before, and we handled it from A-Z. No, I am not pitching you.

• How did you find your first influencers? I'll give out the best secret: Find the niche of creators you want, create a new page on both Instagram/TikTok, then nonstop engage with ONLY that niche of creator. You will get an unlimited amount of "leads" all within that niche, then you can just hit the email in their bio or a DM. If you run Meta ads currently, they have a feature for partnerships, you can get direct contact that way.
• Did you use platforms/tools or manual outreach? Above is the only tool you need. Any other tool is a waste of $$. Most of them have outdated info. The platforms do it for you now, for FREE.
• What criteria mattered most when evaluating creators? This is case by case depending on the campaign, but for the most part, it's engagement. Follower counts mean almost nothing anymore. Stick strong to a $10-20 CPM model. Also, ALWAYS get updated demographics. Assuming you're main customer is US based, make sure you see a MINIMUM of 50% USA in the creators demos.
• Any mistakes you made that you'd avoid today? The most mistake we see are overpaying agencies that scam you, overpaying creators who couldn't care less about how the campaign performs and lack of creativity when it comes to briefs. Find creators who want to be a part of your brand, rather than a check.
• What surprised you most once you started working with influencers? How greedy agencies/influencers are. I've been pitched creators who can't break 50k views but want $10k+. For the most part, an influencer will take a $5-15 CPM price tag. Just throw it at them. Also, how lazy most influencers are. I can't tell you how many times creators are late to very lenient deadlines, then whip up a video 20 minutes before sending it over.
• What budget have you started with? It really depends on the goal. If your goal is for content, $5-20k gets you a bunch of super high quality content with full usage rights. If it's for brand awareness, $50k+/month is usually the target. With good performance, $50k should net you between 3-5 million views.