Without full HTML there might be some issues with adapting to BBcode so I've tried to include some of the links we found helpful on day 1 here.
https://www.seabreezecomputers.com/html2bbcode/ - site to convert HTML to BBcode
http://scriptygoddess.com/resources/proportioncalc.htm - to work out re-sizing images. Remember in the tags it's IMG for a normal image and image=x,y if you want to resize it.
