There's a 5 photo limit directly emailing from the Photos app.
However you can select more than five photos and select Copy rather than Email from the Share menu. Then open an email and paste them in. In this case the limit really depends on the size of attachments your and your recipient's email provider allows.
You can also long press in the body of an email to get he pop up menu, slide the menu to the left and select the option to Attach a Photo. Select the photo you want and then repeat as needed for additional photos. Again the limit is the email provider.
As far as Mail Drop is concerned, I'm fairly sure that initiating Mail Drop is from OS X only. Any device (including non iOS) can receive a mail Drop message and download the content, but it can only be sent from OS X.