BIKE + HIKE + BIKE all in one activity possible?

Yes.. . Just make your own duathlon..... Or Triathlon.... 

In "add activity" ... . then choose "Multisport" .... then choose Triathlon"..or "duathlon" ... then add "bike"  "hike" etc. ..

Hope this helps. 

: - ) 

Yeah, that sounds great!

Now i just need to figure out how to switch between the disciplines during the activity.

Ok, so with the "BACK-LAP" button you can switch between activities.

When i'm right, i can toggle as often as i like between the activities and they get accumulated, right?

You can either create a new activity with the sports pre set that you want to use. With the back-lap button you go to next sport in your activity. But pressing the lap button can't be undone. So if you make a mistake you can't undo this. 

Another option is to change the sport type in the original activity. I do that sometimes when i Run and want to do body weight exercises and run back home. I just start the run activity and when i hold the back lap button (for 3-5 seconds) I can change the activity to workout and after the workout i can do the same and select run again. The watch wil later change the run activity into multi sport. But you'll have to try and see what you prefer. 

The first option is really a show stopper.

The second option would be great but does not work with the back button on my fenix 5+?

Didn’t work for me either, but then I found out I had to select a Hold Button for ‘Change Sport’. By default I think long press back/lap button during activity takes you to the widgets.

Settings -> System -> Hold buttons.

Now it works like a charm

Thank you very much - with the changed button function it‘s perfect!

I definitely recommend using the change sport option.

When I do indoor cardio I use 3 different machines and usually have a set sequence, sometimes I like to vary my routine and using the change activity button means I can start my first activity and then when I switch to the next I just use the change activity button and select the next.

I did try setting up a custom activity with the 3 disciplines but it would does not give you the flexibility in the sequence or number of times you do each activity.

The second option is perfect for the op....

I just tested it after selecting "change sport"as a "hotkey"....... I can change back and forth many times...... and after uploading to connect... I can see all my activity markers..and GPS traces.

I'm keeping the setting now.... I think it could come in handy for me as well.. . Thankyou.

: - )