Easiest way to do this is to apply a texture set to your clothing and modify it.
Since it's for your personal use, you can use any of my clothing that uses seamless tiles and switch out my texture with one of those you purchased.
Click the name of the texture and locate your new texture.
When everything looks right to you, you would then save that specific material as an MT5 (MC6 is for multiple material zones).
Click the + folder to add a new folder to your library for your personal MT5.
Switch to that folder and you're ready to save your new file.
Click the + icon at the bottom of your library panel to save your new material setup.
This will open the New Set dialog.
Change New Set to the name you want for your new material.
Single Material will be checked by default.
For an MC6, you would check Material Collection.
Click OK to save.
That's all there is to it.
You can continue switching out the Texture file with your new Textures and save each one.
To apply, select the material zone of your clothing item, and click your new MT5 material.