As long as you really add value by your work to the Internet, you won't be considered as a spammer. Saw this in a video by matt cut. For eg you post about your gardening site in a health blog, they won't help you, infact they will derank you. So you have to be wise while building links. The best option would be social media. If your posts are good and they get a fair amount of facebook shares and tweets, you can do wonders.
The number of links can be according to competition, if you enter high competitive spot, on first page then you have to build links progressively to overcome the competition, I would say.
i would say 10 to 15 quality backlinks a day are enough ! Its not all about back links anymore ! there is many other factors that matters !
It's not very easy to get so many quality back links. So even if you get one quality back link and you can share good quality content then it would be fine. http://www.online-business-virtual-assistant.com/
Also, if you are building links to your site then these links should send traffic to your website too, if they are not sending traffic then they are not too good links, I would say.