Rainbows is a good idea take as much training as they offer you as it all adds to your CV. Does your uni year finish in May? if so could you volunteer to read with children in a local primary school or help out with trips etc? They dont usually finish until the end of July. However they will need to CRB you and this can take up to 8 weeks so might be worth asking around now so that your paperwork is done before you start.