@meetdilip Certain aspects I can help you with, but creating a theme is something I charge for. And I'm not taking on paid work at the minute.
As for your tiles, that's simple enough, best size I've found is about 450x450, then set the container to cover in the ACP. This makes sure that you don't get the background repeating x when you're on a tablet or mobile which has wider tiles. As for what images you want, that's entirely up to you, but do bear in mind any copyright laws etc, you could try somewhere like dreamstime or even google searching for the image you want, followed by stock photo, or use this website to help you find free images. You can then open them in photoshop, or if you don't have photoshop, GIMP is free (and badly named) and will allow you to crop and change the image sizes.
As for the opening in new tab plugin, I'm not sure, you'd need to speak to the author. I'll have a look at your site briefly and see what I can see.