CAD Design for Bike and Wheelchair Design and Frame Building

Hi I am an software developer and maker, I will need someone to do CAD design job for me to upgrade our existing design in STEP and to convert my design/drawing to STEP files. The CAD design tools such as freeCAD, or solidworks, Fusion 360 or similar should be ok. Need face to face at my shop in Hayward, California. Someone with machining and welding experience is a plus. This job is ideal for graduate student interns. The particular design need for us: (1) modify and re-design our existing frame for prototyping and production, (2) Mesh-based sculpting in STEP files, converting complex mesh data (like STL/OBJ) into a usable CAD solid (B-rep) for editing, (3) create "surfaces from mesh," enabling features like fillets, extrusions, and saving back as STEP for engineering, as STEP holds precise geometry while meshes use triangles, The Challenge: Converting a mesh to STEP while creating solid data from surface facets; converting STEP to a mesh via tessellation. (4) Need skill to move from STEP to STL/OBJ, and convert from STLOBJ to STEP.