Perhaps your first step should be to decide whether you plan to house them indoors or outdoors. It should not be both. Right now, it may seem easy enough to switch a rabbit back and forth (inside to out) since the Spring weather means the weather is roughly the same both indoors and out. But once summer heat comes and then winter cold, the temperature difference between inside and out can be significant. Rabbits cannot easily regulate their body temp when they are being moved constantly. So, for example, moving from a relatively warm house in winter to the cold outdoors every day and every night will be quite stressful on a rabbit.
A rabbit should either be housed indoors, day and night, all the time, (occasional time outside on nice days). OR housed in a safe, enclosed outdoor cage, day and night, all the time. If you choose outdoors, then that outdoor arrangement should be setup as soon as possible (Spring is ideal). This way, the rabbit gets accustomed to the outdoors and will naturally grow a thicker coat come winter. An indoor rabbit will not.
Once you decide which place you'd like to house them, then we can offer suggestions on how to best (cheaply) provide the recommended space.