I'm surprised no one has mentioned ottos, or otocinclus catfish. They stay small, around 1.5-2 inches and are great algae eaters. They are shoaling fish, so you'd need a small group of 3-4. I would add them near the end of the stocking. They need a cycled tank and established algae. They love planted tanks (usually more algae) and will usually eat algae wafers in supplement to the algae in the tank.
In a 35-40g tank I'd go with 2 schools of fish. 3 schools would fit, if you choose small types, but it will look very chaotic. 2 large schools are more appealing. Harlequin rasboras are great little fish. They are very hardy and very colorful. Neons are on the sensitive side. They are very colorful, but kind of boring in my opinion. I keep them, but they aren't very active, like my other fish. Glowlight tetras look similar to neons in shape. They are an orange-yellow color and are more active. Black neons are also pretty active and would be a good contrast to harlequins. Another tetra to check out are lemon tetras. They are very playful and pretty and would also contrast the rasboras.
i think my premliminary plan is to get 2 gouramis, 2 peaceful bettas, and 5-6 each
I'd go with only one gourami. Usually males are all that is sold in pet/fish stores and many times they don't get along. I'd go with one of the larger gourami types, such as a blue, gold, or pearl gourami and just get one. It will save you alot of trouble. Only female bettas can be kept in the same tank, and sometimes even they don't get along. You could try a trio, but its really hit or miss with bettas and gouramis. They share the same space, being labyrinth fish, so sometimes you can have problems. I'd choose either the gourami or the female bettas...or go with 1 male betta if you want...just pick peaceful, non-nippy tetras/rasboras. The ones I mentioned above are all peaceful.
Cherry barbs are peaceful and don't really school. They can be kept in trios of 1 male to 2 females, so you could have them in the tank if you wanted.
what plants should i get?
That depends on how much light you will have over the tank. Compact fluorescent lighting is best, in my opinion, for plants. I'd shoot for around 70 watts of light over a 35g tank or 80 watts over a 40g tank. That would be 2 watts per gallon which would allow you to grow medium and low light plants. If you are up for going with CO2 and all that, you can up the lighting to 3 watts per gallon or more. Check out the planted section...they can help you more on the subject of plants. I have around 2 watts per gallon over all my tanks and grow medium and some high light plants. I like lower maintenance (no CO2).
A good stocking for a 35g tank would be:
8 small schooling fish (type 1)
8 small schooling fish (type 2)
1 gourami/betta or a pair of rams (bolivians or german blues)
3 cherry barbs (1m/2f)
8 cories or 4 small type loaches
3-4 ottos or 1 bristlenose or rubbernose pleco
I think with 2 schools you will be more pleased visually. Having more than 2 types gets very messy looking. I should know, in my 55g I have 3 types, with one type only having 4 fish. I haven't been able to get any more, or I would. It looks very unappealing and takes away from the plants. You see the different types of fish, instead of the plants.