Saftey. There are many bacteria and parasites that reside in soil. Toxoplasma gondii is dangerous secondary to its ability to cross the placenta. If you continue to garden make sure you stay away from any animal feces as well as wear protective equipment to prevent punctures from roses and open wounds that might become exposed to soil. You will be able to garden and have a healthy baby, just be cautious.
No. Early pregnancy comes with no exercise restrictions unless you are bleeding.
Tetanus vaccination! Gardening is fine during pregnancy, with reasonable precautions: get your tetanus toxoid vaccination (due to be renewed every 10 years), wear gardening gloves, avoid contact with animal feces/droppings, wash your hands thoroughly before eating, maintain good hydration and avoid extreme weather and heavy lifting. Best of luck!