Not sure about the other runners here, but in my experience fartlek sessions are usually the from of session/'speedwork' used at the beginning of a season - particularly xc - to ease back into speedwork. I would do that in your first week or two as it is an easier session than 1km reps for sure. The fast portions of a fartlek are also usually a lot shorter than 1km and you build endurance with the easy and mixed pace running in between.
The more typical interval sessions after that are good, although I would say probably 400s are the shortest rep for endurance-based stuff as doing 100s is definitely a sprint session!
Yeah most of the tops designed for trail running (usually also have a half zip) have pockets, look at inov8 as well. Shorts usually have adequate space for gels but if not get maybe an armband pocket; that should fit an asthma pump, or a running bumbagh of some sort. I don't like them so will try and squeeze whatever i need into various other pockets but others have no problems.
Same - I tried L-cartinine f about 6 months a year and a half ago. Made no noticeable difference and was incredibly expensive on a student budget so I stopped. You most definitely do not look like you need lose any weight but cleaning up my diet over a month of the summer holiday made a much more noticeable difference in terms of weight loss, and that was just through eating a it less junk not shelling out loads on supplements! Also read something a bit scary about the side-effects when l-cartinine is converted into TMAO in the body, according to one study it promotes atherosclerosis which was a big concern for me as heart disease runs in my family on both sides! But google that for more details to make up your own mind as it was just one study.
Interesting thing is,that in terms of rewarding regular participation (regardless of time/finishing position) parkrun already has the 50, 100, 250 t--shirt clubs and the Sweatshop monthly prize. I guess then the points competition rewards commitment to one event (despite parkrun nowadays seemingly promoting 'run tourism'...)
Don't race every week, r even every fortnight. That would burn anyone out not only physically but also psychologically. Insomnia and lack of concentration could be due to overtraining. Maybe try cutting down to one session a day?