Hi aleday,
First of all, welcome to Quilting Board! Congratulations on finishing your first quilt top! It looks great!
I know there are a lot of beautiful quilting designs out there, but I've run into too many former quilters who tried to take on a more complicated design with their first quilt and quickly gave up the craft altogether. For that reason, I recommend treating quilting like any new skill -- start with foundational skills & build from there. Being able to enjoy the process
I would suggest sticking to Stitch in the Ditch for your first quilt and just quilt the squares (2 HST's). You will have enough to worry about with keeping the quilt supported & in the ditch without having to also take on intricate designs.
Maybe go with a 50wt cotton thread in light ivory/cream so it blends in with the fabric -- and if you haven't already picked a back, busy prints help hide any little bobbles in the quilting. For 50wt thread, I use a Microtex size 80 when doing straight line quilting; I started quilting on an old Singer Genie 353 from the 1970's. Whatever needle you use, changing to a fresh needle before you start quilting will definitely help. A good stitch length for Singers is 8 stitches per inch (a little under 3mm in metric).
Start in the center & work your way to the right. Then, start back at the same point & work your way left, followed by center to top & center to bottom. The reason for that is to ensure that the fabric/batting is evenly pushed to the outside edges of the quilt, rather than bunching up the fabric/batting somewhere in the middle of your quilt top. As a side note, quilts typically are also basted from the center out. If you plan to pin baste (I do!), I strongly recommend investing in some of those curved safety pins they sell at Hobby Lobby or Joann Fabrics. You can pin with regular safety pins, but it's more challenging. Also, know you'll probably need many more safety pins than you would think. I probably use 300+ on baby quilts. You want to put them about a fist's width apart in each direction.
For stitch in the ditch, you want the stitches to sit right in the seam between the two pieces. There are different types of walking feet available that are preferred by different quilters. With lower loft batting like Warm & Natural, I like having a walking foot with a ditch foot. It has a little piece that extends down & is meant to ride in the "ditch" created when you press your seam to one side (you sew just barely on side that doesn't have the seams pressed toward it -- the lower side). For higher loft battings like Hobb's Wool or Warm & Plush, I prefer an open-toe walking foot because it does not drag on the fabric & allows me to best see where I'm quilting.
Some walking feet come with multiple attachments (ditch guide, open toe, closed toe), whereas others are cast as one piece. The third party walking foot I bought for my classic Singer was all one piece.
Once you've had a practice run or two with doing stitch in the ditch quilting, there are many other wonderful, more advanced straight line or free motion (requires a darning foot) designs that can be learned.
Good luck! Hope you post more pictures once it's quilted. I can't wait to see how it turns out!