Hey Summoner88
1.: I won't adjust my pushing ranges because of the structure. At least not primarily. The most important factors that can alter a range are your opponents, as well as ICM calculations. The structure itself can make a small difference, but in the end it won't change too much for me.
Pushing a wider range is always an option if your opponents are calling tighter then they should (which is the case quite often).
2.: I would simply push according to nash ranges. For 5BB (M of 2) it suggests
22+, A2s+, A9o+, K9s, KJo+, Q9s+, QJo, J9s+, T9s
You may adapt the range to your opponents. If they are calling tighter you can push a bit wider. However, 72o won't be part of my range ever when pushing from UTG with a M of 2.
After the blinds hit me I will still not lose my patience and keep on pushing according to my position as well as my stack. I am obviously not able to deliver you a range for every possible scenario. At the same time there can't be a range that makes sense for all positions.
3.: Without a read I will push fairly tight. However, even with less then 20 hands you should be able to have a read on his play style. If he is a frequent limper I will push very wide with 12BB+. If you have less your fold equity won't be too good. Therefore I wouldn't push extremely wide. Most likely I would just ignore the limper and push my standard open pushing range from this position.
Attention: If a regular starts open limping all of a sudden he will very often have a monster. Therefore you should be very careful in these situations.
4.: Depends on your personal play style as well as your postflop skills and your opponents. Against very active opponents a push might make sense with parts of your range or even your whole opening range.
Personally I wouldn't open push a lot as long as I have more then 15BB.
The ranges depend on different factors again. For example exact position, opponents stats, bubble factor, exact stack sizes. Therefore I can't give you a valid answer.
If you have any further question or need some clarification feel free to ask!
Regards,
Asaban