@tgzzzz, I must commend you for swinging a trimmer at your age...that's great.
I would warn you on your Stihl Kombi...there are three major drawbacks in my opinion, for using this as a trimmer. One is weight of the unit, one is the trimmer attachment itself, and one is the 4-Mix engine throttle. I own two Stihl Kombi KM131R power heads and basically all the attachments, including the trimmer attachment.
1.) First off, weight. ANY split-shaft design is going to weigh a little more than a dedicated trimmer. It also likely will have more vibration as there is a coupler for the two shafts to fit into. I'm not sure which Kombi powerhead you have, but the 131R is pretty heavy.
2.) The trimmer attachment. More specifically, the trimmer head. This head does not hold very much trimmer line, and is significantly more difficult to re-spool new line on to compared to others.
3.) The 4-Mix engine throttle. When trimming, being able to "feather" the throttle through various power levels is important to doing a good job and using the least amount of fuel. The 4-Mix engines have a throttle that is basically all or nothing. Idle or full throttle. It is difficult to modulate to a mid-RPM. For many of the Kombi attachments, this is just fine. I have the paddle broom, the articulated hedge trimmer, the cultivator, the straight edger, the bed edge redefiner, etc. These attachments are going to primarily need full throttle most of the time anyway. But a trimmer only needs full throttle when you are in the thickest of grass. To do a precise job, you need to use low and mid throttle, and in my experience, its hard to do that.
For general trimming, I use Husqvarna 525L trimmers. Very lightweight and well balanced, less than 10lbs. At 1.21HP, they are likely the best power to weight ratio for a professional trimmer available. These are not fatiguing, we use three of them for hours at a time when trimming out a cemetery.
Anyway, best of luck in your ventures.