That is true. But can I run tires without tubes in these rims, or should I grab some sealant too?
Here's the way I see it. You're trying to get a bike going with little experience and not much money to work with.
The people who own bikes with the early cast rims like yours tell us that they don't need to use tubes but have to check the tire pressure often because of leaks. It might be because the rims leak a little or it might be because the valves for cast wheels don't seal well.
The rims are good good enough to use without tubes but you need to use valve stems made for cast wheels since the valve stems are molded directly into the tubes.
There is no problem with the sidewall of a tubeless tire sealing on the cast wheel. There is also no problem with the tire bead staying seated on the rim.
You already have a set of new tires to mount on your bike, so that cost has been covered.
Two tubes will cost about $30 and will have the air valves molded into them.
Two air valves that are made for cast wheels will cost $10 or less.
You will have to buy or build a balancing stand. You will also need to find the weights that you will need to balance the tires. This will cost money to buy or build the stand and get the weights you need. You will also be doing this for the first time so there's more ways for things to go wrong.
A package of balance beads will cost about 10 to 12 dollars and will automatically do the balancing for you as you ride.
Two bottles of Ride-On balancer and sealer will cost about $30 and will balance the tires as you ride plus give you some insurance against punctures.
The lowest priced option is to not use tubes, install tire valves for cast wheels and use balance beads to balance the tires. It will cost $10 or less for the air valves and about $12 for the beads.
The next lowest option is to not use tubes, install the air valves for cast wheels and use Ride-On sealer/balancer. The valves will be $10 and the Ride-On will cost $30
If you use tubes it will cost another $30 to buy the tubes.
It will cost $12 for beads, $30 for Ride-On
You can make/buy a truing stand plus wheel weights and learn something new but will have a more difficult time getting your bike on the road.
So, the lowest priced and easiest option is to not use tubes, install air valves for cast wheels and use balance beads to balance your wheels. You will need to keep closer attention to your tire pressure. This would be the decision I would make where my money was limited.
If you want to pay less attention to air pressure and give yourself some insurance against punctures then you should use Ride-On sealer/balancer, this is the decision I would make if spending another $18 wasn't a big issue for me.
Having to buy tubes then make or buy a truing stand plus wheel weights will probably be the highest priced option with more things to go wrong and more new things to learn. This would be the least attractive choice for me.