Multiple Adsense ads or Single Ad for all?

Hi all,

I am using wp insert plugin for inserting ad code.

Can I create multiple ads for placing them on website?

e.g.

Ad1 - Header
Ad2 - inside post
Ad3 - Sidebar
and so on

OR

Can I use same code with changing ad dimensions?

<script type="text/javascript">
google_ad_client = "pub-ID";
google_ad_width = 336;
google_ad_height = 280;
google_ad_format = "336x280_as";
google_ad_type = "text_image";
google_color_border = "FFFFFF";
google_color_bg = "FFFFFF";
google_color_link = "FFFFFF";
google_color_text = "000000";
google_color_url = "E1771E";
</script><script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>

Which one is advisable?

Using above code is against adsense TOS?

Also which method is good.....adding adsense code with plugin or manually inserting ad code in php files?

Please help me and share your view and experiences.