As and answer to the first question, heater hose should not be used on smooth parallel tube, you need either the serrations present or a bulge, if you wish to use heater hose between the two items I suggest you substitute 2 more hosetails for the stem adaptors, that will correctly cover that end. As for the tube interface I suggest you fit 22mm push fit or compression to 3/4" BSP fittings and 2 more hosetails, that will make a secure permanent job of it.
As for the second question, I see no reason not to do as you suggest, pressures in the circuit are equal everywhere so the PRV will still function as it should, as will the expansion vessel. The filling loop is just for filling / repressurising and whilst the return pipe, close to the Webo is an ideal your suggestion will work well enough. One quick point, if you can arrange a bleed point very close to the output hose from the Webo you could save yourself some grief with air locks in the heat exchanger during commissioning and in the future.