I'll itemize what I think for you.
1. I change 50% of my aquarium water every week; so, I recommend the same for you.
2. Bettas are solitary fish and like to be kept alone. There are exceptions, but for the most part I recommend just one Betta for a 10 gallon tank.
3. Guppies with long fins and Male Betas are a bad mix.
4. Male Bettas love "live" plants. They like to hide and will even lay within the foliage.
5. Do not just dump the fish in another receptacle and clean the tank out. You will kill any or all beneficial bacteria that exists and it takes a while to get a tank cycled.
1. Are you familiar with The Nitrogen Cycle? There is a tutorial somewhere in this forum. I forget where at the moment.
2. Can you take a picture of the spots? As clear as possible please.
3. Are you planning on purchasing "live" plants? I believe plants help the fish to live longer, healthier lives. But, that is only my opinion.