I want to use my VPS web server as a private smtp server for my home

- I'm developing software for my wife's business.
- Email is the primarily transport for communication.
- To date, I've been using gmail for outbound smtp sending of email.
- I've hit the Gmail threshold for number of msgs per day:
       sendmail: 550 5.4.5 Daily sending quota exceeded. f67sm9848964yhi.10 - gsmtp
- I suspect this sending threshold will be an issue during development only
- I develop from my home, and am now blocked by the inability to send email
- My wife's business has a web site running from a VPS outside my home
- This site runs Postfix today for local sending of email
- My ISP (Comcast) blocks port 25 in both directions.

What I want is to also configure Postfix on the VPS web server as an SMTP server for my home, and only my home, so I can continue my work. I believe I'll need to use a non-standard port for smtp. I have DHCP controlled connection to the internet, meaning my home has a non-static IP address on the internet.

I'm not much of an email guy, and really don't want to be (I read manuals all day, I don't need yet another skill set).  Is there an easy(ish) way of setting this up securely so that I'm not opening the VPS web server up to spammers?