This is what we would suggest. I would look for seed that you can buy in bulk from some of the seed companies. Suggestions are Wildflower Farm in Coldwater. Stokes Seeds, Veseys, OSC and many more. This can be done online. You may want to start with a smaller area at first as this can be overwhelming and you do not want to be defeated and give up the first time round. You said you would get rid of the grass and add soil. This is good. I would suggest being ready to plant seed in August. This time of year, we tend to get a nice dew in the mornings and evenings. This will help if you do not want to water every day. You can start in late May, but I have found that the weather gets hot quickly and unless you water everyday you will not be happy with what germinates. I hope this helps.
Thank you for your question J. Reiger.