You went through the effort of giving a well though-out post with a decent amount of information, so I'll reciprocate by breaking this all down, piece by piece, and then summarizing my thoughts at the end.
Originally Posted by creyes
I had been an endurance athlete (triathlete) for the last 6 years. Had an injury 4-5 months ago and had some coaching problems and have decided to take a break from endurance sports.
My nutrition was primarily simple carbs and veggies - not a lot of protein. I was around 5'11'' 155lbs.
Alright, so we've established a few things here--you're underweight, probably somewhere in the range of skinny to skinny-fat, and need to adjust your diet. You recognize that diet change will be the catalyst here, which is good.
I slumped. Kept the same diet and didn't exercise a lot. Put on a ton of weight. A month ago I started getting back in running shape. My 5k is still ~16 mid/low depending on the day. But outside of some leg power from cycling I have essentially no practical strength. Today, 5'11'' 167lbs 19% body fat (fitness scale, accuracy is questionable).
Well I have no idea if that's a good 5k time, but you seem to know what you're doing in that regard. Are you running as much as you were before? Do you want to? What is "running shape" to you?
I'd like to be 175-180lbs @ 9-10% bf. Defined but still being able to run (I'll accept a loss in some time, but I'd like to be able to run a 6 min mile). I've gone a week without grains/legumes/dairy. Focusing on proteins and healthy fats, carbs from veggies/little fruit. Have good whey, am avoiding creatine for now (don't want think the extra pumps are necessary yet), am doing Vitamin C, K2, Grapeseed supplements for now. Have read about and want to try Intermittent Fasting - and have started a pretty basic 4 days a week + 1 cardio routine.
Starches are still going to be very important for putting on muscle mass. Eating big will be a chore. Your reasoning for avoiding creatine is off-base--I'm not sure you completely understand what creatine is or how it works in the body.
1) Should my diet priority be to cut out the 8-9% fat first? Emulate a cut phase for a body-builder and then build after? Or do I eat +calories now and know the fat will get burned?
There are conflicting opinions on this, but I say put on the muscle mass first. Even at your current body composition, you're pretty underweight. Build a strength base with the main lifts and get stronger At first, you should actually be able to put on muscle and decrease fat at the same time, at least to a small extent. After a while, it gets pretty difficult. Put on more muscle and make your body a more efficient machine.
2) My work hours are typically 7 - ~5ish and I'm in data centers a lot so not much flexibility. Ideal IF seems to be eat 12-8pm and fast in between. That's not really possible for me. I feel like IF would particularly help me because my body has been so used to producing insulin constantly that the resistance from fasting would probably increase my sensitivity a good amount. Anyone have good scheduling ideas?
Just focus on hitting good macros and energy balance at first. When you get to the point that nutrient timing is really that important for you, you probably already know a lot more about nutrition than the majority of people.
Thanks for reading and I look forward to any advice!
Don't chase two horses at once. Pick a goal, and go after it like a mother****er. You're going to have to figure out a compromise. Not everybody can be Alex Viada.