Even if your site is old enough, I don't recommend you to use automation software. I'd rather hire someone who can do optimization for my site.

It is more about velocity. It is ok to build 100 link on day 1 but on day 2 you should also make 100 links.

Is that link velocity concept applicable to the whole site, or to each individual page of my site? Say I want to rank for keyword a with the page mysite.com/keyworda. Then I also want to do the same for keyword b with mysite.com/keywordb and etc etc for all the letters in the alphabet. If I build 100 links to the first page, and then 100 links to the next page etc etc will the search engines catch on?

CONSISTENY. This is what you should consider if you decide to use automation softwares. If you build 20 backlinks in the first few days, then build 20 in the following days. But if you build massive backlinks, shall we say around 1000 a day, then also build 1000 in the following days. Be consistent. Certain fluctuation in the numbers could trigger penalization from Google.

Best regards,
Jesus

just use it. Experimentation with it will teach you the right way and youll pick up some stuff along the way that only you know.

You'll hear different things from each person. Most don't even know what they are talking about. Trust me, just do it. If you are really scared, then try it slowly. Start with sick, then move to sen lite and so on.

If it harms your site then you just found the best trick in the world!

Multiply what you did by 10 and blast your competitors as well so they get removed from the serps!

Nobody will tell you how. It's the unspoken law of IM.