Research Papers / Research Sample category/description/type advice [3]

Hi, I'm busy with my first research proposal paper.

My Target Population I have put forward as :
Employed people aged between 18 and 55, who work with computers daily for at least 5 hours. They should also have as a minimum intermediate levels of skill with computers and be proficient with English.

OK, so now in the next section I have to describe my Sample and I'm not sure which method or type it will fall under, or which best to use for my situation for example: Probability vs Non-probability. Simple random, stratified random, cluster, systematic, quota, convenience, purposive, snowball).

To explain how I thought of going to work recruiting these participants (+-30 people) was with a simple online placement, think Craigslist, and then if the person meets the criteria I will include them in my study. I am hoping to have a nice age and gender spread and have a random element to it.

Questions surrounding this :
If I exclude people, even though they match the criteria, does that influence my sample type?
What happens if the first 25 people are all aged 25 (Thus my reason for my wanting to start excluding some applicants)?
Not sure if I should receive like 200 applications and maybe select from there manually or randomly and what that would means in regards with the sample type?

Thank you
Any help will be much appreciated!