You only need a static address for hosting email or VoIP.
You can do just about everything else with DDNS (dynamic DNS). However with DDNS, you will have downtime until the DDNS update takes effect and propagates to clients. This can be seconds... or hours. Depends on the DDNS service and TTLs that they set and how quickly your script/DDNS client works to push the update out.
You should check how often your address changes and check how quickly your DDNS solution pushed the update out. If it's 10 seconds every 10 months, you will likely find that perfectly acceptable. If it's an hour every other sunday... maybe not. But only you will know how much downtime you can tolerate.
I always will take static IP personally. But it's not technically required and you can work around it if you want to save the 10-15$/month.
Edit: You could also argo tunnel if you're okay using cloudflare. But I don't think that answer is particularly in scope of the question. But just in case it's useful to someone out there I'm adding this edit. Doesn't fix the PTR requirement for Email and VoIP stuff though.