Which Blog Type you are working ?
If it's magazine then 7 recent post and feature slider with 4-5 post.
or else if you a static page and you can add upto 7-10. but if you have a large thumbnail like 600px width and 300px height then use 5 for better page load and even you used CDN !
I used 7 recent post in our homepage. and tag archive as 10 and category wise 10. if you are WordPress using blogger this will help.
My blog loads in 2.5s to 6s depend on the theme also !