I found this 3D plant model
The model does not carry any textures, or more precisely, it will never be loaded automatically, so you always have to assign a texture manually. Some models you find on the internet consist of several textures, of course this does not work when loading it into the game, so you have to split the model into several submodels (there is always the rule: 1 texture per model).
It's better when a model has proper UV-mapping, so all different parts are just on a single texture 
Be aware that some models you find on the internet don't have any textures at all, but just consist of different colors in combination with some effects (those models are usually not intended for games). In this case there is no way to get them into the game (you can still load the model, but there is no way to transfer any color information or effects into the game).
Btw, according to the image, this looks like a high detail model. Although there is no triangle limit in the game, you have to make sure that your models don't have too much triangles, otherwise it will have a big impact on performance. Models for games usually don't have that much triangles, but a lot of models you find on the internet are often ultra-high-detail, which is fine for rendering purposes, but not suitable for games (e.g. when a plant has hundreds of thousands of triangles, it will cause a massive drop in framerate already after placing just a few of them).
Several free online 3d models,like trees for example, have the leaf texture and also the trunk texture
If the leaf texture and the trunk texture are two separate textures, you have to load the leaves and the trunk as two separate models.
lets say that the average size of a 3d model is 10Mb
10 MB is quite a lot. This indicates that the model has probably an insane level of detail. As a reference, a maple tree in Rising World has around 6200 triangles, the filesize of an obj would be around 500 KB only. Or the current piano, an obj file would just be around 15 KB.
Will the addition of a great amount of models drain the game performance
Biggest problem would be the bandwidth. All data have to be transferred from the server to the client (of course this doesn't apply to singleplayer), but when the client has to download several GB before joining a server, it would be quite problematic
But if model files are really that big, it indicates that they consist of too many triangles, and this would result in poor performance...
Actually WBB changed the way how links are handled, the capitalisation doesn't matter at all, but the query structure (the ? after "index.php" instead of /).
But I'm sure that it will be possible to add new animals etc. in the long run.
Ohne dem Wasser etwas an Dynamik zu geben klappt das nicht so richtig. Es wird also leider noch dauern, bis sowas in greifbarere Nähe rücken wird...
