The image in the custom header looks bad

The cropping tool in WordPress does not always give the expected results. Try sizing the image in a graphics program to the size of the custom header. The size is given on the custom image header page. Not all images are the same pixel size so check it out. Upload the resized image and you should have a better image.

Why is there more than one font type on my site?

It may be that the site was created by typing the text into the content field for the page. You may have also copied other text from a word processing document. If it was pasted directly from the word processed document it will display the font of the original document. If copying from a word processed document us the Paste from Word tool on the toolbar, then the font type will be consistent with the design for the site.