I use Costco with good success. I mainly use them for 8x10s and larger.

If you want the their prints to match what you see on your monitor do the following.

Calibrate your monitor. My x-rite color munki recommends a luminance setting of 120 for led monitors and at this setting the prints are much darker that the monitor. I lowered my luminance to 90 and now the prints match the monitor for density.

Go to https://www.drycreekphoto.com/ and download the profiles for your Costco. You will find all the information on their website installing the profiles and how to send the photos to Costco.
Follow their instructions and you will get matching photos.

I built my computer 3 years ago. My main work is photo shop and light room. When I looked into the best processor for photo shop I learned that photo shop only will use 4 cores. Of the tests I read at the time photo shop seemed to work faster with Intel vs AMD. I went with the Intel I7 best I could get at the time. I loaded the memory to 32gigs as well. Look at what software you will be running and make sure you get a processer what will work at best speed with that software.

For a portrait try this with the person back to the sun. You will need a silver reflector. You can purchase one or make a poor mans reflector. Crumple up foil and then open it and place over a large piece of cardboard. Have an assistant hold the reflector to bounce the sun back to the person. Watch the subjects face when the reflector is at the right angle you will see their face light up. This will balance out the light ratios for you.

Another way is to use a large diffuser panel. This can be a large white shoot through umbrella or a white shower curtain liner stretched over a wooded frame. You can now turn the subject to the sun Have your assistant hold the diffuse striking your subject is gong through the diffuser. This will even out the shadows on your subject and give a very pleasing light.

Every one who has replied has great information. The purpose of a printer profile is to get the best color balance from the paper and printer ink set. Each paper responds differently to the printer. To take advantage of the printer profile you must use software allows you to set the printer profile for your printer. Both Epson and Canon come with profiles for their papers. You can also download these from their web sites. Much was said about Red River Paper and I very much agree with all the comments. I use a Cannon Pro 100 printer and use several surfaces of Red River Paper. My personal opinion and experience is they one of the best papers on the market. Their web site also has fantastic information on printing, and using printer profiles. As mentioned by others you can download their profiles to match the paper and printer you are using. Take some time look over the information on profiles and printers on their site. Even if use a different brand the instructions will help you in learning how to set your software and printers up for printing

Keep in mind your camera, graphics card, monitor and printer each have their own interoperation of what color should look like. That is where the calibration and icc. printer profiles come in. These allow all devices to see color the same.

The goal of all the following steps is to get your prints to match your monitor as close as possible. These are the steps I follow...
1. Calibrate your monitor. http://www.xrite.com/categories/calibration-profiling/colormunki-family or http://www.datacolor.com/photography-design/solutions/display-calibration/ make great devices to calibrate with.
2. In the software you are going to printer profile to the profile for your paper and printer combination. The example I give below is for Photoshop CC
a. from the file menu select print
b. this will bring up the printer set up dialog box.
c. click on the printer set up button. Here you will set the paper size, type, and quality setting. Look on red rivers paper web site. you will find examples and how to set these for your printer with their paper. You also need to turn off the printers control of the color. Again there instructions on the Red River web site.
d. you need to change the color handling from printer manages color to photo shop manages color.
e. the next box is where you set the printer profile to the one you downloaded and installed.

This seems like a lot of work but once you learn it is very easy. You will get prints that match your monitor. I truly feel monitor calibration is a must if you are going to produce high quality prints. Good luck in your photographic journey.