First, may I welcome you to Tropical Fish Keeping forum.
Second, the heat issue. I would suggest it is better to limit the fluctuation as much as reasonably possible. A full 10 degrees every day is significant. The aquarium will usually be the same temperature as the room, or very close; the larger the volume of water the longer it takes to warm and cool of course. Sudden changes are not advisable, which is why I would not use the ice method. Better to let the tank warm to the room. Opening the cover and using the fan is fine provided you don't have fish that are likely to jump--and you'd be surprised at how many will.
Third, I see a real issue with your intended stocking. We have fish profiles here, second tab from the left in the blue bar across the top of the page; if the fish scientific or common name used in the profiles appears the same in posts it will shade and you can click on the name to see that species' profile. I recommend you check out the fish species. I will only point out a couple of issues. Tiger Barb
are notorious fin nippers, and sometimes they can get downright nasty to other fish. Long-fin fish such as Betta must never be in the same tank. Also, a group of at least 8, preferably 12 or more, will usually reduce the nipping/aggression. But this would fill your 36g, as this is sufficient space only for a good group of TB. If you want other fish, I would forget TB. And Betta are not community fish; other fish tend to nip at them, or they attack other fish, it depends upon the species and the Betta's temperament. Puffer are also aggressive and should be on their own; and some require brackish water, others are freshwater. No shark is suitable for a tank as small as 36g, and they are territorial (and thus "rough") to varying degrees depending upon species. Several are in our profiles, under the Cyprinids category.
Cycling. Do you have live plants? This is the best way to "cycle" a new tank. Any other method is highly stressful on the fish, and will lead to internal problems that will affect the fish either in behaviours or health down the road, and in almost every case cause a premature death. The effects of ammonia and nitrite poisoning are substantial, at very low levels. You can read more on this in a couple of articles here, one on cycling itself "stickied" at the head of this section of the forum, here';s a direct link: A Beginner's Guide to the Freshwater Aquarium Cycle
And the other on bacteria from the Freshwater Articles section, here's that link: Bacteria in the Freshwater Aquarium
These will help explain the dangers.