I'm a relative noob when it comes to all this stuff but I thought I would throw my opinion into the ring for your consideration. Take it or leave it.
I've consistently had a 3.0 system for years, with front left, right, and a center channel. Certainly this is an improvement over the speakers in any television. Depending on where my wife and I have lived, we have added left and right surrounds. A nice addition to be sure, but we could do without in a pinch.
After I joined this forum a few weeks ago in search of ideas to improve the quality of my living room theater sound, I picked up an older but reasonable Paradigm sub locally on Craigslist for $50. This sub is pretty mediocre but it is the single most impactful addition I have made to my home theater in ten years. It has increased our enjoyment of movie and television considerably. Now I cannot wait to upgrade to the next tier in quality. I hope you will consider that as your build your system--adding a sub to your system is a big deal and if waiting on surround speakers will help you get there faster, then so be it.
A couple of points...
1. You have chosen the right place to ask for help. The people here possess a wealth of knowledge and are friendly and good-natured to boot.
2. Take your time putting together your system. No harm in spreading out the cost and getting quality affordable gear. The good news is that this stuff lasts a long time.
3. Look at Craigslist in your local area for stellar deals. If you see something that look promising, ask about it here and people can give you idea whether or not it is something worth pursuing.
4. You will be very happy with the Denon 1613. I have owned a Denon AVR-591 and now own a Denon AVR-1712, slighly older siblings to the 1613. I have been very pleased with their features, performance, and value. I think you will too.
Good luck! Have fun!