Yes, always cover them with a tarp to protect from sun until you finish the walls.
Water is not a problem, but prolonged sun exposure will destroy the polypropylene material of the bags.
Once you finish the walls, you will cover them with 2-3 good levels of adobe and you will not have anymore this concern.
When you fill them, do not use dry dirt, have a moisture, like 5-10% water. Not too dry, not too wet, enough to be able to mold them in good shape. Also the moisture, once is evaporated, will leave the bag hard like a rock. Once is covered in adobe, there's no concern that will melts like sand.
You need to do your own tests, depending on the dirt you use, its composition of clay, sand etc. you have to see how much water you add or not.
When I got few days raining, I had to wait 2 days with sun until the dirt had the right level of moisture to be able to put it into the bags.
That's why this construction could take long time because not always you will have good weather. We re I live is raining enough per year so I can't build all seasons.
Don't believe everything is posted on YT. Most of those channels are designed to get your attention and make money from views.
Very few are real constructions as you see... Behind those scenes there's a lot that you DO NOT see.
My advice:
Do it yourself, with your own mind, hands, materials, like you dream it.
Don't try to copy any of those YT bullshit videos.
Only like that you will see how is it and what challenges you may encounter.
But once you finish it, it will be your most rewarded thing in your life.
Been thinking about this for a couple months actually and eventually plan to do some variation of it. The "traditional" method of home buying in the US is stupid and wasteful, with fiat also pricing much of the younger gen's out of the market while many of the others lose whatever financial flexibility they had with the mortgage. I'll sleep in my damn car if it comes to it before getting pinned down with it.