If you get tired of turning off comments in each entry you can just turn off comments for the whole blog in the Settings tab on the left. This will not cause existing comments to disappear. If you accept comments you will get spammed. You will have to add a captcha system as well as making users register and be approved as well as authenticating them as well as approving every single comment. Spammers are pigs. The will hack your site, no matter how obscure it is.
If you need to enter a table you are better off authoring it in Komposer or some WYSIWYG editor, and then past the source code into the entry page. You first hit the goofy <A> tab in the editor to switch to html mode.