Established brand launching on Amazon – pitfalls to avoid?

Finally taking the plunge and launching on Amazon UK and USA (FBM) after being in business 3 years but seeing diminishing returns in both organic and Google ads (especially the latter).

Working on the A++ now & storefront before hopefully launching in 7 days.

I’ve learnt amazon ads are a must to get things rolling – are acquisition costs in 2025 cheaper than Google and what’s the most cost effective strategy to run ads on say a $40 daily budget per country?

Just concerned with having to burn lots of money before seeing results.

Any advice / pointers to succint online guides much appreciated!