There's tons of Blender tutorials out there. What I've written below is advice that I hope will be helpful if you either already know a thing or two about modeling or just start trying tutorials. It might also give you some search terms.
If you're making clothes, I suggest starting with only a few polygons (say three: front, back, one side), adding a mirror and subdivision modifier, then extruding and adding loop cuts as you go. That way you only add loop cuts as you need them, and build topology that's as clean and efficient as you can make it. Over time, you'll probably find you need fewer and fewer polygons.
The big things to keep in mind when making clothes are seams and edges. First of all, it's easiest to UV map your clothes so the islands match a sewing pattern, and your UV seams match where you'd have real seams. Once you have those islands,, you want their edges to be as smooth as possible so you can put a nice even hem on them. So try to keep any poles (vertices that join a number of polygons besides four or two) away from your hem. For instance, if you're working around breasts or shoulders, you'll probably need a pole or two. But you can have a row or two of polygons around the edge that make a smooth boundary.
Also, if you're making clothes, remember that you can use the cloth modifier. For instance, if you want to make a simple shirt, all you have to do is model something pretty plain and stiff, then let it drape. Blender also allows you to
sew clothes now, sort of like Marvelous Designer, so you can look into that, too.
The skin modifier is very cool, but if you're making anything dynamic or conforming, you need to watch how you use anything that automatically creates topology. For anything static, it doesn't matter, but if it bends or flexes in anyway, then you need to watch where you put your loop cuts.
If you're working with Poser, it's best to import figures directly from the Geometries folder. You can work at any scale as long as you're consistent from importing to exporting (for instance scaling up by 10 going in, scaling down by 1/10 going out). That said, I find it really hard to make people-sized items that _aren't_ clothes without considering real world scale. 1 Blender Unit (BU) = 1 meter. Using Poser's meter scale, the scale from Blender to Poser is about 2.6125 to 1. That makes a conversion back scaling down by 0.3828. I usually fudge and use 2.5 and 0.4 respectively. That said, I've decided to use 0.3828 for non-figure related props, because my scenery (chairs, stairs, etc.) often comes in a bit too big. For clothes, jewelry, etc., it kind of doesn't matter because I'm measuring against the figure itself and not really relying on hard measurements. But I find that doesn't work as well for table legs or even flowers.
One of _the_ strongest aspects of Blender is its polygon modeling capabilities. It's really easy and fast to extrude, make loop cuts, etc. Add the
F2 add-on, and it's even faster to fill in spaces and extend grids. If you select a vertice or edge and CTRL + click, you automatically extrude your mesh in the direction of a click. Want to make fancy designs? Just make a small box and start clicking away like you're drawing. Same works for the skin modifier. Want to make a tree from scratch, without using sapling? Start with a vertex and just start CTRL clicking away to make the skeleton.
If you want to do procedural modeling (making weird geometric shapes, for instance), then Blender's not so great. But I have more clothing meshes that I can count that haven't been made into sets. It rarely takes me more than a few hours to model a whole set of clothes in Blender. It's everything else that's time consuming.
IMHO, the second strongest aspect of Blender is its sculpting capabilities. Especially if you have a pen and tablet. You can find tons of great tutorials out there about sculpting. There's also a (paid) retopo tool to make it easier retopologize a sculpt, but Blender does have built-in retopology tools that work (just not as easily). That said, I personally avoid that practice and prefer to have a nice strong base mesh with good topology before sculpting. I'm not advocating that way, because the industry standard is sculpt then retopo (though mostly people do this with Zbrush). It's more that I can't really speak on using sculpting that way, despite its growing popularity.
Given your spending constraints, Blender's also likely to be by _far_ the easiest way for you to paint 3D textures if you want or need to. If you map clothes right, they're _way_ easier to map in a 2D program. And Blender's 3D painting tools aren't nearly as controlled as Photoshop's 2D tools or Zbrush's 3D ones. But they are good, and better tools are expensive.
