Set multiple keys at once with global-set-key?

In a word, no. C-h f global-set-key tells you what the function's signature is:

global-set-key is an interactive compiled Lisp function in subr.el.

(global-set-key KEY COMMAND)

Give KEY a global binding as COMMAND.

...

The function accepts only a single key sequence and a single command.

If you really wanted to save multiple occurrences of the text (global-set-key and ) then you could write a function to do that. E.g.:

(defun my-g-s-k (&rest k+c)
  "..."
  (let (key cmd)
    (while k+c
      (global-set-key (car k+c) (cadr k+c))
      (setq k+c  (cddr k+c)))))

(my-g-s-k "\C-o"    'forward-char
          "\M-o"    'backward-char
          "\C-\M-o" 'forward-line)