Yes you can leave it uncovered ,I sewed on a pillow case , and I lay a small tea towel on top each day , they poop a lot ...
If you have a cooling rack just lay the pad on top , I have even placed the heating pad on top of a cardboard box and inside it ...
You’ll be fine the first batch is the most stressful...just set it up ,and check them often
Have fun
Post pictures of what you’ve got so far if you’d feel better
They need their feathers to control their body heat , first they get wing feathers , tails , back then head ... they’ll look so silly but you’ll know when all the baby fluff is gone .
If you can have the heat out there they can go anytime .
And just my opinion but a heat lamp is not a bad idea I use them most of the time and have had no issues , just use a chain to securely hang it and I place a broom handle threw the hook across my brooder box and duct tape it down , it’s held up two ways .... it’s been used for 100’s of years