If it is one person with the amount of luggage you mention you can not travel by train. Trains have quite a generous luggage allowance but it is not unrestricted and more than that, you have to get your luggage on and off the trains yourself in a short time. And your luggage should not block the aisles in the train. Knowing the troubles of traveling with one bike and a little luggage I am sure you will not be able not to block the aisle with the luggage you describe.
In that case the option rental car or van might be the only one. To avoid the drop off fee you can return the van to the place you rented it and go by train without luggage, which does not have to be the same day.
If you have a friend or partner who travels with you you might be able to get away with traveling by train. On a Friday, with bikes, you can not use the train before 9 am, so the train starting 8:58 will not do.
In Germany you can (almost sure) not use the fast trains.
The best you can do is to go to the German rail planner site and enter your details.
This site can sell you the tickets, self print or even in their app on your smartphone.
But while they have an option to search for traveling with bicycles, I can not get it to work right now. (Might work later, might not work at all, you can call them.) This option is under further options.
As far as I remember you can not take bicycles on the fast trains in Germany, so I selected the option no high speed trains (but they do now, see comments under this answer, allow a few bikes each train, so do contact the German railways and ask if important to you.) That will give you a connection of trains where you have to change 3 or 4 times and with a travel time of about 5½ to 6½ hours, with only a few options within that time frame.
I doubt this will be cheap but if with two people and getting the cheapest tickets the German people can find you, you will beat the price or a rental car plus drop off fee.