1. I prefer my jam not to be too sweet and I especially love the tartness of rhubarb, but I urge you to taste your jam during the cooking and add more sugar or lemon juice, depending on your own preference.
2. I didn't blend the jam as I like to have bits of fruits in it, but if you prefer your jam to be of a more consistent thickness, then once your jam has reached the desired thickness take it off your stove and with an immersion blender blend until there are no more strawberry chunks (the rhubarb bits tend to fall into tiny pieces quite soon).