I can't see the pictures for some reason, but I am very happy that you changed to this setup. Unfortunately there are some problems with your plans.. bettas are tropical fish that need stable temperatures of 78-83 degrees to be comfortable, healthy and active.
Keeping them at room temperature can have both long-term and short term consequences that could seriously harm your bettas. Keeping them at lower temperatures weakens their immune systems, leaving them susceptible to parasites and bacteria. Being cold-blooded, it also slows down their digestion, causing bloating, constipation, and consequently, swim bladder problems.
You need an adjustable heater with a good thermostat.
Also, 30% water changes once a week are not sufficient for keeping an uncycled tank. Fish constantly excrete ammonia through their gills, kind of like urine. If this ammonia is allowed to build up, it can actually burn the fish. Constantly having to drink in, swim in, and breathe in pee all at once sure doesn't sound nice, does it? But there is an easy solution.
When an aquarium is filtered, it can undergo a process called the nitrogen cycle. This is the process by which the aquarium is colonized by beneficial bacteria that break down the poisonous ammonia into nitrite which is also poisonous, but that can be broken down by yet another kind of bacteria into a compound called nitrate. Nitrate is much less poisonous than ammonia or nitrite, and can remain in the aquarium within a certain range until it becomes poisonous.
If you got a filter, and cycled the tank, you could go along with your plan of 30% changes once a week. However, if you do not get a filter and choose to not cycle the tank, you will have no choice but to do at least two changes a week--one 50% change, and one 100% change. The reason is this, if the fish is constantly excreting poisonous ammonia and you do one 50% change one day, and another 50% change the next day, inevitably there's still ammonia left in the tank. The only way to get all of the ammonia out is to do a 100% water change. When you do a 100% change, it's important to take everything out of the tank and clean it with hot water to be sure that all of the toxins/waste/uneaten food has been removed.
If you get a good liquid master test kit, you may be able to work out a different water changing routine that will help keep up with your ammonia levels, however, unless you cycle the tank you will still be stuck doing 100% water changes. A good liquid master test kit is a must for anyone who keeps fish.
Also keep in mind that many fish store employees/proprietors shouldn't be trusted--they will say whatever they can to get you to buy things, and they won't necessarily be good for your fish. They're motivated by money, don't forget that. Many of them also go by "old school" fishing methods which have been debunked. It is very important to do your own research--I highly suggest researching the nitrogen cycle and if you're thinking of getting a filter and a heater later on, it's a good idea to look for product reviews before shopping.
I also suggest buying your products on http://www.fosterandsmithaquatics.com
-- they offer flat rate shipping and prices that are marked down $10-$20 lower than any pet store.