Great present!
It's all about you as far as pace goes. Your pace will be based on you cardio engine (i.e. how well you turn oxygen into energy), your leg strength, your technique, your comfort, and the wind! Other than that it depends on if you are riding in a pace line or solo and the wind! Oh I might have failed to mention that the wind plays a big factor.
Seriously, there are a lot of factors in determining a good average speed. For me, I feel short changed if I fail to see a 2x on the front of the average speed on my tri bike but feel real lucky to see a 12 on my mountain bike.
For a newby I would challenge you to find comfort and try to average 15 mph for an hour (cover 15 miles not just average with the bike computer they do not average time spent at zero). It is not a real fast speed but can take folks some time to get there. While you work to get there, work on hand positions; top bar, brake hood and in the drops. Get a feel for how the bike handles in all these positions. You will find a favorite but you need to be equally comfortable in all positions. Start to get a feel for how you attack the wind; and better, take advantage of it. The worse winds are those that hit you at around 30-45 degrees from straight on. Within a short amount of time you should be in the 17 mph range and from there it is all about training and riding time.
Get comfortable on the bike taking water, reaching for a gel and even more importantly, looking around to check traffic.
Learn side of the road maintenance. Learn how to change a tire and carry the tools, tube (2) and pump (CO2) to repair a flat. Bring a small bike wrench so you can tighten a loose screw. Always check your bike before riding off. Make sure the wheels are secure, tires are free of defect and have the proper pressure and that the brakes are working. You do not want to get to your first intersection and find that you cannot stop. Your bike will love you better if you wipe it down after every ride. Nothing pedals easier than a clean and well lubed bike.
Find a group to ride with and learn how it feels to ride in a group. This is not necessary but it will teach skills that might not be otherwise learned. You should develop some comfort riding in a group of other bikes. It is scary as #$#&% at first but you will quickly learn how to ride with others around. Its not that difficult but does require a skill set and communication with others so that road hazards are avoided. The direct benefit of this is cutting wind resistance. A group of riders can ride considerably faster than a solo rider.
I would start to wear your HR monitor now. Do not worry about what it is saying use it for statistics only. Make a mental note of your course and speed and then compare that with HR.
Finally, if you do not have one
get a helmet and wear it. Every time. No questions. Even down the drive and to the mail box. All it takes is one small incident and bang you go down. I went 8-9 years before a big crash but in 2009 I had three. Two broke helmets. Also, wear gloves while riding. They ruin the tan line but the padding provided during a normal ride help to cushion the jolting felt along the road. Also a great pair of bike shorts is worth the cost multiplied.
Finally, be friendly. We (bikers) have a right to the road but it is only a right, not a gift. Wave, talk to riders as you pass, smile at the truck who is miffed by your presence. Make it a point to ask cyclists on the side of the road if all is well. Call out debris and intentions when riding in a group.
Sorry, went long but I am really excited that you have a bike and want to get you headed along a good path. I see a lot of folks this time of year in my area that are truly clueless. They have a bike but nothing else. I have stopped and changed flats more time than I can count several on bikes whose riders neverthought about a flat. All it takes is a really bad ride or two and your new bike will be a dust collector hanging from the ceiling in the garage.