if you want to keep maintenance to fortnightly then you should stock roughly 1" per 1.5 gallons then from there keep an eye on your nitrate levels, if they regularly come above 40ppm (assuming your tap water isn't high in nitrate) then you need less fish or more maintenance.
ok my comments on your proposed stocking, firstly it's too much, you need to go for less species and better groups of them
(2 X Clown Loaches)
(1 X Bristlenose Catfish)
(1 X Peppered Catfish)
ADD
1 X Peppered Catfish
2 X Zebra Loaches
4 X Threee-Line Cory
2 X Verniculated Synondonitis
8 X Helequin Rasboras
2 X Pearl Gourami
2 X Zebra Barbs
you should keep clowns in bigger groups really, i'd get another, but bear in mind as they get bigger they will massivley eat into your stocking, however they're very slow growing so you should be able to either reduce the stocking in this tank or get them another bigger one in a few years before it becomes a problem.
i'd stick to just 1 sort of cory and get a group of at least 6. They'll be much happier. As others have said, get less species and better groupings, honestly it'll look loads better and your fish will be happier.
I wouldn't put gourami's and barbs together, as others have said they'll get nippy.
Your also quite bottom heavy, especially bearing in mind the amount of space the clowns will need as they grow, what I'd do from that list is
3 clown loaches
6 cories
8 harlequin rasboras
2 pearl gourami's
I know that might not seen like a lot of fish for that size tank but it's all I'd put in there unless your prepared to step up the maintenance to weekly.
