Quickest path to recover ability after layoff

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I am looking for advice on the best way to regain my fitness after a long bout of time off. Also, need to lose some weight. It has been some six weeks since I started cycling training again.

1 - For improving power fastest is it better to ride longer at zone 3, like nonstop 1+ hours, or zone 4 in multiple 20 minute intervals?

Right now I have fallen into the habit of doing zone 3 training sessions rather than what I used to do, shorter zone 4 intervals (2-3 x 20 minute duration).

2 - Only a few weeks into my return I find it hard to push myself consistently at zone 4 like I did before. Have you found it takes time to build up that ability to push hard after a layoff?

3 - For losing weight I have a feeling that long (2+ hour) moderate zone 2 rides are the best choice. Does that agree with your experience? I am dreadfully slow in hills now because of these extra kg's. Alreay I am watching what I eat, so the nutrition aspect is in order.

4 - Last item. How would you structure your overall time? 1/3 in zone 3? 1/3 in zone 4? 1/3 Zone 2?