I got a test box at home I'm trying to setup sendmail in. I bought a
domain and host a website on that box. I get dynamic IP from my ISP
which gets updated via DynDNS for the website. I added the MX for my
domain with Google and it's been working fine (I can send receive
mail). But I want to setup sendmail & friends (clamav, mimedefang,
spamd etc.)  to get familiar with them.

I understand that having a dynamic IP and not having a reverse DNS
working to mail.domain.com would put me in the block list pretty soon.
I am not considering hosting outside.

Could sendmail's smarthost be the best option in this scenario? If
yes, should I point it to Google or my ISP? Is there any other option?

Thanks.