Apart from everything others have already mentioned on not keeping goldfish with tropical fish or in too smaller tanks, i have some pointers on your tropical selection of fish;
a. Keeping male bettas with guppys is not a good idea, more than often the betta will attack and kill the guppy due its bright colors or the guppy will become aggressive towards the betta and nip its long flowing fins, so a very risky mix and not advised as it most often ends in tradegy.
b. male bettas do not make good community fish or do well in large strongly filtered tanks, tetras are also agressive towards bettas. With female bettas you can be more flexable with them in community setups- they generally lack the long flowing fins of male bettas which usually cause so many issues for the males and the females can also live together if kept in groups of 5 or larger- you cannot mix male and female bettas together, males and males or females together safely in small groups.
c. The loach you are referring too i think is a clown loach- yes these fish do grow to over a foot long and it is posible to have one or 2 in a 55gallon but this isn't totally advised and it also depends alot what the tanks dimensions are too i.e how tall and long it is etc.
d. As for guppys, these fish belong to the livebearer group of fish which include mollys, swordtails and platys amoung others and they do have a reputation to breed on a regular basis- female guppys can store sperm for up to 7 pregnancys so even if you have an all female group they can still produce offspring and a single female can have up to 30+ fry(baby fish) once a month.
If you go for a mixed gender group you will need to get the gender the ratio right for it to work successfully and not have over-aggression and harrassment to each other- idealy you want 1male per 2-3 females(this goes for all livebearers apart from swordtails where it is near imposible to have 2 males living in the same tank without them fighting no matter how many females you get), although you need to increase the female ratio by one for every extra male you add after one.
You can keep also guppys in all-male groups but these tend to have issues.
If you realy want the male betta(no matter what type), i suggest you get him his own 5gallon tank for himself to live in.
Have you heard of cycling tanks? i suggest you do a fishless cycle in your new tank and there is alot of info on how to go about this in the pinned articles at the top of the beginner section of the forum- cycling a tank is a very important step towards keeping healthy and happy fish.
Apart from heating, lighting and a adequete filter for the tank, i realy advise you buy some test kits that test for ammonia, nitrate and nitrites as this vital in maintaining good water quality, and good water quality can make the difference between a dead fish and a sick fish and it is very easy to mess up; test kits are the only way to actually know for sure what is going on in your water quality.
As for gourami's, these realy aern't my area of knolege but i know they are a very varied group of fish with a large range of temperments and alot of how well they fit into community setup is based on what type of gourami they are, so you will need to find what type you are interested in to know wether it is suitable for the tank and what types of fish to live with.
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ok then i musnt ov seen that sorrry
