Feel free to use fencing, feed buckets, water buckets, straw bales, cones, garbage cans, any sort of barrels, tires, cinder blocks, etc. If you need any ideas, feel free to message me. I have a slew of "redneck" ideas =D
And for the spray painting, use colours. If you ever go to a show, there's no guarantee that the poles will be white. Colours get your horse used to sdtrange looking thingers.
And for more poles, some ideas could be broom, pitchforks, rakes, pvc pipes (although they can splinter and cut your horse, just be cautious), branches, logs, etc.
Just get creative =D