I'm starting up a new blog and the last time I submitted the blogs url to google and other search engines.
But is it really necessary to submit the url or will google and other search engines find my blog on their own?
It's not necessary. Just get some backlinks to it and google will find it. Actually it's better for google to find your site on it's own.
It would be better that you use webmasters tools of Google to list your site there because in case of any problem or if you will avoid any search engines rules or guidelines then google will send you email that you should avoid this step for continue ranking in SERPs.
I do not think its necessary. I suggest you to do social bookmarking of your all blog post in high pr SBM sites which helps to crawl fast in Google.
To add websites in google webmaster tools helps to crawl all web pages faster to index them in google search engines.
Submit your blog on high quality social bookmarking websites, directories.
Google will crawl the url automatically, but in order to get get quickly index your url, you need to submit them to Google.