You need to create your own default template. Open the blank template & set up your document with the line spacing, margins, headers, etc. as you'd like. Redefine all of the paragraph & character styles to have your desired font. You can set default wrap for any object as well as many other settings. Insert a table, click in it & choose the font, size, color, etc. you want in the fonts panel or format bar. You can do similar changes to inserted objects & text boxes. While you're at it resize the box if you want, set the amount of extra space in the wrap inspector, etc. Delete each text box, object & table after you've set them.
Now, save this document as a template & select that template as default in preferences. If you decide to make any changes to the template down the road, just Save As Template again with the same name & replace the previous version. All of your new documents will have these settings for inserted objects, images & tables. Unfortunately, the settings won't apply to any other templates or "foreign" documents you open with Pages.