I have worked with Saint Expedite a couple months ago, there is no need to ask him if he wants to work with you, and I think that’s the case with most saints.
In my experience (though it wasn’t about money) with him it’s better to be more specific with the task, not just generally “improve my financial situation”.
I had a specific opportunity regarding being able to rent a cheap but great flat before anyone else got to it, so I asked him and Saint Jude to work in conjunction on this specific issue. I did this the day before I managed to get it.
About the offerings, yes I wouldn’t miss flowers, add pound cake and you’re good. I don’t think he would turn away if you simply add a glass of water as a third. 
Also, I have taken to using Lady Eva’s method and it works wonders for me as I prefer not to use many tools, for you it’s specifically this part but I recommend you do read the rest of it:
Another thing, a great source of information on a lot of Saints and various pseudo-saints is Judika Illes’ book Encyclopedia of Mystics, Saints & Sages, tons of info and legends on a lot of spirits!