Update your blog as often as you can. Depending on your industry this can be every 15 minutes (if you're a news and current affairs blog), it can be daily or every few days. Some people do it once a week or once a month. If you're using a top blog package like WordPress this will notify Google and Technorati (and many other sites) each time you make a new post. This will bring all of these sites to your site and if you're content is good it will get crawled and indexed. So the more your post the more you get crawled and the higher you stay in the SERPs. So blog as often as you can but only when you have GOOD useful new content to blog. Don't post for posting sake and don't post if you're just going to add nothing to the topic. Fresh quality will do you very well
There's no specific rules that says when you should update your blog. If you can find time to update it everyday, that should be the best.
It depends to you! But of course, If you want to gain tons of traffic, fresh and quality content is your key! So I suggest, always update your blog.
I would use RSS feeds plus some automated content methods along with manually updating and keep it consistent, if you do it daily then keep doing it daily, or if weekly then do it weekly.. basically it depends on your readers / visitors, if you want them to visit often or subscribe then tell them to expect weekly updates etc.. but if you are running mainly adsense etc then daily content would the way to go as G loves frequent updates.. if you're running adsense then make sure you promote the hell out of it using social posting etc.. good luck
When ever you are ready with fresh and quality content you can post. There is no rules and limitation for posting into your blog.
If it's a new site, it's enough to post once a week. When the things get serious, at least 3 times a week.
I would advise to do it atleast twice every week and once you have decent traffic you can decrease it to 1 per week.