In my experience - which includes clubmates' anecdotes plus personal experience of getting ITBS on my right knee and making all the classic mistakes to prolong recovery, followed by ITBS on my left knee the following year but recovering much more quickly, I found that if you stop at the very first sign of ITBS pain and rest from running for a week, then you can get away with resuming normal training if pain free after that rest. However if you try running through ITBS pain at all, then you need to rest for several weeks until it's pain free, then rest for a couple more weeks after that. 6 weeks seems to be typical in this scenario.
Attempts to resume running any sooner usually result in the cycle of repeated short rests and aborted painful returns that end up costing more time than if having just stopped at the first sign of ITBS.
So I would say defer til next year if you can, as it does not seem worth wasting a VLM place if you know you cannot do yourself justice. Then work on fixing the root cause of the ITBS, whether that was glutes, hips, TFL, upping mileage too quickly etc, and get stronger for the comeback.
But if you're desperate/committed to doing VLM this year in particular for whatever reason, you could probably get round, but be mentally prepared for it to be painful, disappointing and/or slow. Good luck in whatever you choose to do.
If you do go ahead with it this year, I personally would not recommend an 18 miler 2 weeks beforehand; an experienced higher mileage runner might be ok with that, but if that's your longest run it sounds like an exercise in boosting confidence but to the detriment of your condition for race day.
Can you please advise how possible this would be and also what training would be required?
I had similar times and improvement to you when I first started training vaguely properly (43min Mar 2012 to 39:30 in July 2012), having had a football background before that. Whether your sub35 in a year goal is possible will depend upon various factors, including - where you are now on your improvement curve vs your natural potential/speed, - how well you manage to train, - whether you have any extra body fat to lose.
For example since I made a similar improvement to you above, I've 'only' taken around 50s per year off my 10K PB (now 36:4x), and having to train more and smarter each year, sub35 still seems like a world away, and from my experience I would say your goal sounds rather ambitious unless you're running that 39:23 whilst carrying a lot of surplus weight. On the other hand a clubmate last year went from sub40 in February to sub35 in September after deciding to shift focus from triathlon to running, so yes it is possible, but who knows how much untapped potential you have?
As for appropriate training, I'm not the best to advise seeing as I'm still celebrating my sub37 let alone sub35, but I'd agree with others that it would be a good idea to mix up the speedwork, eg alternate weeks between 400m, 800m intervals and hill reps sessions. Your current training sounds pretty well structured for a noob (much better than mine was back then), here's one example plan you could borrow from though: http://www.halhigdon.com/training/51124/10K-Advanced-Training-Program - generally the more you read up and learn then the better you'll understand how to adapt the many plans and suggested sessions out there to suit yourself and fit around your life.
I'm 6ft 1 and weigh 11 stone. It's mainly other people who are commenting on my weight loss. Part of me thinks they just remember the "A-Level and University Era" me of almost 10 years ago when I discovered beer and kebabs....
I suspect you're spot on with that. I'm slightly shorter than you at 6ft, weigh around 10 stone 4lbs, with 30 inch waist and am healthy, but I was 13 stone and in 34 inch jeans after 3 years at uni. It's mainly people who remember more what I looked like then that seem to comment, especially the ones who would like to lose fat but don't. I remember being pleased to get back into my 32" jeans, and surprised when I had to ditch them for 30", but similar to Lit's experience it stabilised and I've been a similar size/shape for a few years now, still getting fitter and faster without losing any more weight, and most people are used to what I look like now.
If you're comfortable with the way you are and you feel healthy then it would be a shame to put on weight just because you feel pressure from how others perceive you.