There is not backlink limit, I think also. When you add your site to free directories, there is not problem also, because you can submit page to 500 dirs a day, and then nothing, but your page will be approved in dirs, maybe for next month
safe from what? If you have a good site and you are getting backlinks and not spamming then you can have as many as you want.
Well, has anyone ever seen an emerging website get penalised after going viral, with thousands of bloggers blogging about it etc in the matter of days? You guys can prove me wrong and dump a million or so backlinks on my new domain for the sake of the argument if you want
It's completely and totally random. The search engines will not find all of the ones you got today, today. If you get 10 a day for a week (70) it may take a month before SE's stumbles over them all. If you get 10 a day for a month (300) then it may take another month for the search engine to reflect that change. So if you are doing 10 a day, Google may find 9 today and 11 tomorrow, or none today and twenty tomorrow. Unless of course you are getting all of your links from high traffic sites which will likely update daily.
If all the links are natural its bound to be inconsistent. You write a blog post that gets 1000 links one day and then gets none the next day.
All I can is if you have a legit way of getting any amount of links you want any day then I'm very jealous. To answer your question, as long as the links are natural you shouldn't have anything to worry whether you get 1000, 100, or 10 a day .
For a single site 100 links are safe.now you have to deside no of links are needed for per day for a single site.