Generally, loading half a dozen posts of average size is sufficient, though with smaller posts, you can load more. Putting a picture or two in the blog is not a bad idea at all, but a picture in each post will slow down its loading significantly. Be aware of the possible problems - and various solutions.
Loading the entire blog, on the main page, is not a good idea. If you do this, you will eventually run into the one known size limitation on Blogger blogs.
From Settings - Formatting, check the Show setting. You can limit the main page size by days, or by posts. It's your choice - but think of your readers. Many don't have scandalous bandwidth, nor are the Blogger servers overly robust. When your blog, or even a single post, takes 2 or 3 minutes to load, your blog needs tuning.
There is no need to show all of your posts immediately - if your blog is well designed and written, then the last few posts should give the casual reader an idea of what the blog contains. Blogger offers us several features, that provide good alternatives to publishing the entire blog on the main page.
Note if you set "Show" to "7 posts", you'll get a total of 7 posts. If you set "Show" to "7 days", you could get anywhere from 7, to any number, of posts, displayed in main page mode on your blog.
As you become more skilled in developing your blog, whether it's a Classic blog, or uses the improved Layouts format with all of the new amenities, remember to keep it simple. Eventually, we will see design limitations, besides the limitation in main page view size.
Loading the top of the blog with ads is not a good idea either. When the reader opens the blog, he should see content. Don't let the ads overwhelm the content - the top of the blog should contain no more than 1/3 ads, and 2/3 content. If the reader sees as much screen space taken by ads as by content, the perception will be that the blog is there purely to serve ads. Most readers will go elsewhere, when assaulted rudely with ads.
When is a web page too long? That's subjective, really. But look at how long (high) a page is. Take this page, for instance. You can measure its height, in one of 2 ways, depending upon the page height, the size of your display, and the amount of your patience.
- If your screen is large enough, stretch the height of the browser window, exactly until the scroll bar disappears. Now, measure the height. That's the simplest way.
- Look at the tab in the scrollbar, that you can "grab" with the mouse, and pull up or down, to make the page scroll. How high is the tab, in relation to the height of the browser window? If the tab is 1/2 the height of the browser window, you'll find that the page being viewed is 2 x the height of the window.
Here's an example. Looking at this post, Limit The Size Of Your Main Page, before I add this discussion. When displaying this post, I see that the scroll tab is 1.125" high. The screen is 7" high. Scroll all the way to the top of the page. Now hit the "Page Down" button. How many times do you page down, before hitting the bottom? I count 5 times, on my screen. That means that the page is 6 x 7", or 42" high.
I don't have a lot of patience for counting, though. If the scroll tab is less than 1/10 the screen height, I'll have to count over 10 to page from the top to the bottom. So I prefer to measure the scroll tab height, and calculate page height. Screen height squared, divided by scroll tab height, will also give you the height of the page. In my case, 7 x 7 / 1.125 = 43.5". OK, I eyeballed the measurements very roughly.
Either way, we're looking at between 3 and 4 feet of height. For my little post here, and that is from before I published this addition in it.
Now, I'll use the width of the scrollbar as a reference. It's .125" wide on my screen. If the scrollbar tab is also .125" high (or square), on a 7" window, that makes the web page 392", or over 30 feet high. I regularly encounter web pages where the scroll tab is square, or even rectangular (less than .125" high). Even 30 feet of text is going to take more than a few seconds to load. Many web pages of this height (and I have encountered more than a couple) contain high bandwidth graphics, besides being 40 - 50 feet high.
I would guess that somewhere between 2 feet, and 30 feet, is too high. Bigger - 40 - 50 feet, is absolutely way too high. Very precise numbers there, Chuck. Maybe the best I can say here is, the next time you're loading a web page that is taking too long, calculate the page height. See how high is too high, for you. Or the next time that you (or your readers) have trouble loading your blog, look at the main page size, and cut it in half.
Note that this setting applies only to the main page size. There is no similar setting, to control the sizes of archive or label retrievals - those are limited to 20 posts / page, as a fixed setting.
(Update 2010/02): This month, Blogger introduced Auto Pagination, which will limit pages sizes, automatically - and which should make Blogger more reliable, for everybody.