Hey Byktory085,
Good call to put something on your soil like straws so your soil doesn't dry up fast.
When did you gave water when you took thoose pictures? Because your soil does look nice wet to me. Make sure you do not overwater your plants.
You might have to consider giving less then 500ml because you now use thoose straws.
Yes you can just water on the straws.
Burry your meter 15-20cm deep for now and you will be fine.
You can always learn the weight of your pot by just lifting them up, after a couple of times, you know when she is light or heavy, so you know when to give water.
Like Organoman said, you can always put your finger 5cm into the soil, when putting your finger out and you have wet dirt on your finger, you know she still has water :)
Overal your plants look fine to me,
Goodluck growing :)