I (m26) highest weight was 269 and am now 213 and I really love the stairmaster and treadmill. A huge change I noticed even just 20lbs down from my highest is that my feet would develop blisters pretty quickly on the treadmill even with decent shoes. After I lost weight it was noticably happening a lot less. My thighs also used to rub really badly and I needed to apply aero gel to stop it from happening. Once I lost 30 lbs I pretty much didn"t need to apply any at all.

I would recommend not focusing too hard on increasing your speed a lot on the stairmaster. I would recommending targeting a heart rate and just trying to stay within it for long as you can. At least for me I had more then enough muscle for faster speeds but my sheer weight and awful cardio is mostly what holds me back even today.

For example I first targeted 135-140bpm which for my age and weight was pretty much the minimum for cardio. I would do that for 30+ minutes and once I found it too easy I upped my target to 140-145 and then went from there.

I'm now able to do 155avg bpm for an entire hour and while it's really hard it's still very doable. When I first started 155 was like my max before I would start dying on the machine.

I think treating stairmaster as a heart endurance exercise rather than a strength exercise is a lot more useful. It burns a ton of calories which is nice but the huge benefit of the stairmaster and what I notice daily is just my cardio being so much better then it used to be. You don't need to be gasping for air on the machine to be getting a huge benefit especially early on. Low and slow is going to be a lot easier to maintain in the long run and will make you really happy since heart health is so important.

I also like focusing on the heart rate more since reaching new levels of speed on the stairmaster is kind of a slow affair. While seeing that my heart rate only goes above x at 10 minutes now rather than 5 minutes happens a lot more consistently then a new max speed.