Just seen step over pear trees growing locally how any years before they fruit.
Most of the suppliers sell very young ones which are effectively an espalier with just one layer and you will need to make a post and wire system to continue to tie them in and prune them properly. I would estimate it would be 3 years before they would have grown enough to begin fruiting. You can buy older ones which have been pre-trained and those are very expensive but should fruit within a couple of years (you would remove any fruits the first year after planting to allow them to establish their roots.)
Thanks very helpful would you consider it a good idea to get self fertile ones
Yes, or two different varieties. I think you can even get 'dual espaliers' with two varieties grafted onto one rootstock. You'd need to check with the suppliers that where the graft is made would be low enough for training as step-overs though.