Customising clothing is a good way of up-cycling or changing the design of clothes that you don't like any more, are bored of or even damaged. There are many ways you can do this, from simply sewing on patches to getting creative with fabric paints depending on what look you are going for.
If you are looking to imitate a particular style just do a bit of research to give yourself some inspiration. But If you are looking to come up with your own unique look you could do a few sketches first to come up with your designs.
If you want to add pockets, zips, buttons or trimming to your hoodie, look in fabric or haberdashery shops to get the right materials. For patches and badges etc. There are many online outlets to check out, like Ebay or Amazon, if its a band name or logo try a local alternative clothing store or again, online. If you can't find what you are looking for, paint the design with fabric paints onto some calico
you could also have a go at using the fabric or parts of other clothes to turn into new parts to go on your hoodie, like to line the hood in contrast colour.
Here is an example of adding embellishment to a hoodie.
Or you could be brave and cut up the hoodie you intend to wear!
As far as if it is a good idea or not, I'd say get creative and go for it!