You need a heater, a filter preferably. You shouldnt put any bettas together. male or female in a tank of that size. I recommend getting Silk Plants or Live Plants..
They can't be preganant. They are an egg laying species. And who knows she might just have a full belly.. That little white dot occurs in all of female bettas it is called the ovipositor
6 is a good number but 4-5 is the minimum IMO in a heavily planted tank. This tank should be a minimum of 10 gallons. I have a sorority right now with about 10 females. Its a larger tank.....
BUT. Back to the original question. No you should not mix species. The requirements are different...
Too small. The fish are gonna be stressed. Ammonia will build up too quickly which in turn will stress or even kill the fish. I'm pretty sur eyou have a 10 gallon right? Put the fish in that tank
lol. I would have done that too! sadly I dont have any cherry shrimp though as to start a colony of 5 it would cost me alot of money. they are expensive here
I wouldnt get a betta if you have guppies. since guppies generally have long fins and bright flashy colors bettas will most likely see them as a thread and harass or kill them. If you do want a betta a little desktop 5 gallon with a gentle filter and a few broad leaved plants along with a heater...