I do this annually and you are on the right track. A planted bird deal is always a great option as it works for all levels of hunting...key is to know your clients expectations - do they need more catered to or not? Do they want to shoot a lot of birds or just get out and enjoy some time away and a nice meal? An example is me - I do not like golf nor do I golf well. However I will go on client golf events and enjoy hanging out, having some drinks etc....so if you spent a ton on me to the fanciest course or took me to the local country club, it would not matter to ME. However to some, getting to just see some course, might be a great experience. Knowing your clients will guide the HOW you execute the event, where, and what amenities. Not everyone "hunts" the same....I have guided these events for others and hosted them myself....and that key of how you do it and what emphasis on activities need to be catered to the client. Just like getting kids into hunting - make it a good experience for them. As mentioned above, these events are about relationships - finding common interests, sharing some time, etc. Spend MORE focus on that. If a work topic comes up, it does, but these always go better if the focus is on the relationship. Then as mentioned, you have a relationship that is not just a transaction, and that lasts longer.
That said to "expense" the trip, I have seen some sales reps have to give a SHORT presentation (was an ag chemical rep I believe with a bunch of clients) and he just made it as casual as possible and literally told the guys "hey in order for me to expense all these drinks for you fellas, I gotta pull up the powerpoint so just give me 5 min)....I was just watching from the bar as a guide, but the team took it well, listened to him for 5-10 min, he wrapped up and they went back to dinner drinks and socializing until midnight. So it can be done - would just not make it an agenda item if you don't have to.
Definitely recommend some clay shooting ahead of hunt (day before, morning of, etc..) - it not only gives practice but also lets you see how clients handle firearms in the field. It perhaps gives you a chance to work with them and improve their shooting which in turn improves their experience. But it also lets you find the ones that you need to watch out for and catch safety issues upfront....then they can get caught before the heat of a moment of a point and flush. I used to guide some hunts for a non-profit group (not to be named) that awarded trips....and those were some of the scariest days afield I had for me and my dogs. But then we incorporated a clays event prior, and we were able to guide/fix/adjust things much better and safety infractions in the field dropped dramatically.
To your other questions - sometimes for a specific client, maybe just you and them? Maybe you see if there is someone they want to treat and bring along from their company or family...you don't want where they just bring their buddy they hunt with regularly). Other times, it might be great to treat a bunch of clients at the same time - again depends on interests, your budget and what you are targeting. Feel free to ask more, but it more should be structured with what you are trying to achieve.