Others have covered on possible ways you can tackle the situation , hopefully you will get through this. since you have stated that you don't have a dedicated

Others have covered on possible ways you can tackle the situation , hopefully you will get through this. since you have stated that you don't have a dedicated sysadmin , its better to use a platform like Heroku to host your app. I am not suggesting that it will make your website/app inherently secure, but at least it removes a lot of pain points.