Lindsey, you sound a lot like me. My loss was early, too, and I was devastated for a while, but I just felt like I had to dust myself off quickly. I admit that I did not work out for a few days afterward, but you should do what you need to help relieve the stress. I didn't use a tampon with the bleeding. I took it easy while the bleeding was heavy and just made sure I was near a bathroom. (I absolutely hate pads!) Mine ended up being heavier than a normal period but only lasted about as long as a typical one. So I hope yours is the same way.
OPKs - since it's your first cycle using them, I recommend you start after all your bleeding and spotting has stopped. I personally use them once per day (usually in the early evening). When I start getting fertile CM, I pick that up to twice per day (morning and evening). You're probably fine just testing once per day, but I think for the first cycle, it's nice to see how long your surge actually lasts and get a feel for it all.
Keep in mind, too, that this cycle will probably be weird. I had a lot more CM throughout my cycle following the loss, including 9 days of watery/EWCM leading up to O, which is unheard of for me. It's just something to keep in mind.
Charting would be a great idea. It's how I learned that I have a short LP, which was most likely the reason for the loss. So using OPKs and at least charting temps will really help you understand your body better. If you end up having an LP issue, I'd be happy to answer any questions you have about that.
You might also, if you're not already doing so, take a baby aspirin every day. It promotes blood flow to your uterus, which can help both with conception and with preventing clots around the placenta if you do conceive.
Good luck, Lindsey. But also definitely take the time to grieve. We're here for you.