Looks like my tank has a water volume of about 5.2 litters so I need to lower my water changes to about 2.5 total litters a week.
I am uptown, so I was going to edit my OP, but it wont let me. In fact, I don't have the ability to edit any post as far as I can tell. Could someone tell me how?
So here are the changes I would have made to the OP.
The Story:... (yall can go back and read it)
The Facts: The tank has a volume of 1.8 gal at the water level and about a 1.4 gal water volume.
It has a...
1. Plastic Plant
2. Small rock
3. 2/3 inch of aquarium gravel which was coated with something to make it colorful and non-sharp pre-purchase (unsure if it is regular size or not. It could be smaller)
4. Tetra filter made for 3 gal
5. Hood with LED light (also near south-facing window, so lots of indirect light)
6. Tetra 2-15 gal heater (keeps it a constant 76 degrees)
7. Thermometer
Partial water changes will now be done 3 times a week (2x removal of water and 1x gravel cleaning using turkey baster)
Diet is Tetra BettaMin Tropical Medley once daily. Possible future variance will be done on Sundays.
Original OP Question: Considering the size of the environment, the level of care given to the environment, the filter, and the tankmate, what would be a good fish or invertebrate to place in the tank with him?
Answer: None at this time.

>If the tank is increased to 5 gal, I may add a snail or a few shrimp.

>At 10-15, I may add some of the fish I desired. Suggestions were Cory Cats (schooling so several required), kuhli loaches (controversial as some sites and posters say minimum tank should be 20 while others say it would be fine), dwarf cory catfish (4-6), mollies (controversial as they can be bullies and need aquarium salt which can harm Betta), livebearers, or African Dwarf Frog (controversial as can attack Betas or visa versa).
Question 2: What would be a good heater for my tank?
Suggestions: Hydor Theo 25 watt with adjustable temp control, 7.5w heater, and a few other wattages.
Conclusion: Cold front caused an acute temp drop in Gus' tank. None of the heaters suggested were available at the local store, so a Tetra 2-15gal heater was purchased. The tank has stayed a constant 76 degrees since the heater was introduced.
Question 3: Real plants or fake and if real, which ones?
Suggestions: Real are much better than fake because plastic can harm fins. Real also keeps water quality higher and keeps algae down. Fertilizers are good, but not required especially for beginner plants. Watch for discolored leaves. Possible plants are Java fern, Java Moss, Anubias, Hornwort, water sprite, or Marimo Moss Ball (must be turned a few times a week)
Conclusion: Moss ball is most appealing at this time because of tank size as well as the locomotion the ball possesses which can provide enrichment for fish. It is also soft and can be used as a Beta bed. Other plants may be purchased when I am able to upgrade the size of my tank as all suggestions would make good additions. I am still trying to decide on a secondary choice just in case they are out of Moss Balls.

>Java Moss looks to be an insanely fast grower which worries me. More info needed.

>Java Ferns are interesting and beautiful, but why wont fish graze on it? And i wonder if the light my tank gets would hurt it...
>Anubias would be GREAT for the larger tank!

>Hornwort is a great plant... but I would rather have different leaves. Possible secondary plant in larger aquarium.
>Water Sprites are beautiful and I would love to have one in my tank now, but it is a crazy fast grower. I must do research on how I would keep it under control. Suggestions?
Question 4: Is it okay for fish to sleep on the heater?
Answer: Yes. Betas like lounging on things. Consider a Beta hammock for a future purchase.
Question 5: What are good treats and foods?
Answer: Betas are insectivores, so look for foods based on that. Beta flakes and pellets which contain meat/insects are good. Live food, Bloodworms, pea (controversial because they are insectivores and have short digestive tracts. Hybrid conclusion? 2 a month would not cause harm), flightless fruit flies, mosquito larvae, or Brine shrimp.
Conclusion: Will shop for freeze dried insects or attempt to catch larva after more research is done. Insects will be fed once a week in place of flakes and about half a pea will be given 1-2 times a month as a deterrent to digestive issues.
Question 6: Is my tank size bad?
Answer: Not ideal, but as long as water changes are kept up and the fish is healthy and active, it will work. 5gal is best. 2.5gal is a healthy minimum size with room for enrichment. Anything below 1 gallon is unethical and cruel to the fish.
Question 7: How much water should be changed out weekly?
Answer: 50% tank volume. Water volume is about 1.4gal = 5.2 litters which means about 2.5 litters a week total.