Let the numbers guide you. 

Being new to this, what are some known strategies that people use to purchase a second, third, fourth property quickly [within a couple of years] opposed to waiting for that single property to bring in enough income to afford the next purchase?

I have spent a lot of time reading through guides like Brandon Turner's How to Estimate Future CapEx Expenses on a Rental Property and How to Buy a Small MultiFamily Property: A Step by Step Case Study, which have been incredibly helpful. 

As I am earning relatively well in my job I can afford to service the 15 year loan and the debt is being paid down relatively quickly.

Please click on the links, give them a read, and share your thoughts in the comments.First is a post that I feel will help not get overwhelmed with the amount of info that is here on BP:https://www.biggerpockets.com/blogs/5868/52761-the-simple-guide-to-getting-started-on-bpThe second is a post that will help get you focused with your real estate investing goals:https://www.biggerpockets.com/blogs/5868/52743-im-new-to-bp-any-advice-would-be-appriciatedThe last one is a post that will help you choose an “investor friendly” real estate agent.

I had a quick question, what is the criteria you look for in property?

Please click on the links, give them a read, and share your thoughts in the comments.First is a post that I feel will help not get overwhelmed with the amount of info that is here on BP:https://www.biggerpockets.com/blogs/5868/52761-the-simple-guide-to-getting-started-on-bpThe second is a post that will help get you focused with your real estate investing goals:https://www.biggerpockets.com/blogs/5868/52743-im-new-to-bp-any-advice-would-be-appriciatedThe last one is a post that will help you choose an “investor friendly” real estate agent.

I'm very new here too, but I recommend you to start reading the free Guide provided by this website.

@Kim Meredith Hampton Kim, sorry to bother you but have another quick question and wanted to see if you had any information on it. 

Even if you get a wholesaler or flipper in her area to quickly purchase from her, you don't want her to get taken advantage of.