Otho thank you for asking this very important question before doing.
The first part of the question about the sports logo's you would be correct about, that is a no no you are not to use sports logo's with out written permission of the owners of those logo's
The second part of that question about changing the logo is iffy at best, one also needs to remember that even team names tends to be a registered Trade Mark which also makes it a no no to use.
The patterns posted here do not fall in the public domain. They are posted by the designer for the public to use free of charge but the designer still holds the copyright to them. As far as using the patterns to cut an item and to sell that cut item. In most cases it is ok to do so but you need to read what is on the pattern. For example you will find that some patterns have "For personal use only" or something like that written on the pattern. In this case (the typical intent) the designer is saying you can use the pattern to make a cutting but you may not sell that item, but you may give the cutting away as a gift. If you have any questions about a pattern and its use, contact the designer for clarification. For example a number of my early patterns I have for personal use only on them not really understanding what I was doing. But if someone contacts me about one of them asking for permission to sell the finished product I tend to give them the ok.
As far as posting patterns that you did not make, anywhere, is also not a good idea as most designers would take offence to that. You can contact the designer and ask for permission to do so, but in many cases thay are going to tell you no. With me it will be a case by case basis. The best thing to do is simply make cuttings and post pictures of your cuttings and place a statement along the lines that you can cut a variety of different subjects, that if they don't see something they want all they have to do is ask.
I hope this answers your questions, and remember when ever you have a question about a pattern ask the designer or post your question here. Again thanks for asking before taking action, much respect earned from me for asking your question.