Suzy, let me just start by saying the sewing machine is great!
I think one big thing about art related stuff, is sometimes parents can put kids off drawing and things by (the parent) drawing things the child can't(iyswim)like my husband draws cats and people for my younger daughter(who is 3.5), so she is never confidant to try and draw by herself, where as my older daughter(who took a great art class in the USA where the teacher told me this info) started drawing at about 3.5, her own people and things because I would never "model" any drawing(not draw any recognizable figures and labeling them), I would scribble along with her. I had this great book with all this info, it was called something like teaching art to young children. It covered how all these marks and dashes kids do are pre writing skills. Also another thing I firmly believe to give a child confidence(and to encourage the motor skills) is art at this age should be "process" oriented instead of "product" so they should be making art to enjoy the process not to have something pretty to hang on the wall(I am not saying these things apply to you and your son but these are things I feel strongly about and find my younger daughter's nursery is not very good about them. I have witnessed an aid telling her she didn't put the sparkles on a star right! and if I walk into the classroom and see one more "project" with the teacher doing more then the children, and it being hung on the wall to resemble a nursery ryhme I am not sure what I will do!!!)
Easels are a great thing for a kid to have(one thing everyone I knew in the states had that I haven't come across much here in London), if you find you can trust your child to only paint on the easel and not the wall next to it! you can have paint one day, crayons the next. I seem to remember that the angle(upright) helps fine motor skills. You could also just hang paper on the wall. Also huge roles of paper down a hallway is fun to have as a long term art project, something I did when I owned my own house(but can't do now we are in rented accomidation!) But I am one of those people who doesn't care if the house is very "kid" based
Beading is also a great thing to have a child do to help hand eye coordination you could find large beads with big holes, or you can even used dried pasta.
Glueing things is a great project, you can use lentils and rice and beans, or small bits of paper, and any little bits and bobs you find. Buttons, packaging, sticks. Put white glue in a dish with a paint brush to incourage holding the paint brush(which is like how you hold a pencil)
I have a recipe for homemade playdough, which my kids always loved to help me make(we would put glitter in it) Also I have another book with all sorts of art ideas for young children. If you want I will dig it out, maybe they will have it down there?
Lastly, marking pens in different sizes(think and thin) are great. And my all time favorite activity is oil pastels on black paper, kids seem to love the way they write(thick and smeary) and that they can "write" on black paper.
HTH