I’m sure you’ll be fine. You know all the points that you are contesting.
Did QDR give any indication whether they will attend the hearing?
One of your strongest points is that the original claim was never served within 4 months. Make sure you emphasise that at your hearing. There is no discretion on the court to allow an unserved claim to stands. I was very surprised when the set aside judge allowed it. I can’t remember if that was even brought up at the set aside.
On the day, arrive early enough to get through security and let the usher know you have arrived. Remember to ask for costs for unreasonable behaviour when you win. You can prepare a costs schedule for your time spent on this matter at the Litigant in person rate of £24/hour.
Time spent on research, preparing your set aside, defence, WS etc all count. Also, any travel expenses to and from the hearing are also allowed, such as transport, parking etc.