Another good report, thanks!

Some things to keep in mind:

A blast marker is gained as soon as an order is failed. This may break a unit, preventing a 'hold' action, and will also suppress units if they choose to shoot as their hold action. In the game this means your Stormtroopers and Valyeries would have broken when they failed their order, and couldn't have rallied as their hold action.

A broken unit can immediately make 2 regular moves when it breaks. This can help get it to safety, so your Russ's may not have had to die from all those blast markers. If they fail to rally in the end phase they also make 2 regular moves, not 1.

Your Commissar in the tank company was Fearless, and Fearless units cannot die due to blast markers. That may have saved your BTS, as it's very hard to chase down a Fearless, 4+ RA save model.

Chaplains are also Fearless, and Fearless units cannot die to 'hack down' in close combat. Think of it as losing combat causing you to break (as it does), then each point you lost the combat by being a blast marker. The Fearless unit ignores those blast markers (but can't 'take a hit' for someone else- basically, distribute the hits as if the Fearless models were not in the combat).

Space Marines have And They Shall Know No Fear. You used that correctly for suppression*, but it also affects losses from blast markers and 'hack down' in combat. Basically, it always takes 2 blast markers to do what would take 1 blast marker for someone else- 2 markers to suppress, 2 markers to kill from a broken unit, and 2 to kill from combat losses (losing by 1 in combat causes them to break but suffer no extra casualties).

(*) Suppression is not a choice. Suppression happens back-to-front in the same way that casualties happen front-to-back. That makes placement important as you want your best shooters to survive, but also not be suppressed, so they'll usually be in the middle of a formation. Models must be in range and have a shooting weapon in order to be suppressed, but it doesn't matter if they can hurt the target or not- even models with a small arms weapon (not able to roll dice with normal shooting) can be suppressed for this purpose.

Your Thunderhawk would probably have been in range to contribute supporting fire to the Assault Marines.

When a combat is ongoing (from a draw result), all casualties previously inflicted in that combat continue to count for future result determination. In other words, if casualties were 5:2, but the combat drawn, and the second round saw casualties of 4:2, combat resolution would be worked out by counting casualties as 9:4.

Space Marine Terminators have 'Macro Weapon, Extra Attack +1' as part of their equipment list, not as part of their notes. That means the 'Macro Weapon' effect only applies to that extra attack, not all of their attacks (so they have 1 regular 3+ attack and 1 MW 3+ attack each). This is important if you ever play with Eldar- Most Aspects gain special rules through equipment, not notes, so attached Exarchs and Autarchs don't gain the equipment benefits, but do gain the notes benefits. As a specific example: Howling banshees gain first strike by a piece of equipment- the banshee mask. An Exarch joining that unit has +1 attack, but doesn't gain the equipment bonus, so that extra attack does not have first strike. Warp Spiders have first strike in their notes. An Exarch joining them has +1 attack, that does benefit from first strike.
I've forgotten the character that was with the Terminators (if there was one), but if it had an EA+1 it wouldn't have gained MW unless the character specifically came with that (eg. Chaplain).

For the Thunderhawk and Assault Marines- this is tricky. Basically, the best way to think of it is that the flyer and transported units are a single formation until the end of the turn. The act of landing and unloading the Assault Marines used both the Thunderhawk's and Marine's actions that turn. Since the Thunderhawk was doing a land and shoot action, the Assault Marines could have shot at the same time the Thunderhawk did (to no use, obviously). In order to get the Marines into combat immediately, the Thunderhawk needed to do an Air Assault. It would need to land within 15cm of its target, unload the Marines (up to 15cm away since they have jump packs), then the entire lot would fight in the assault, counting as one formation for all purposes. The Thunderhawk would have no chance to shoot regularly. Once the combat was lost on the second round, the Thunderhawk would have been immediately destroyed as it was a grounded flyer that lost an assault (air assaults can go very wrong!).

The rocket pod of the Valkyrie has Disrupt, and it hit a marine. That means the target unit immediately gained a blast marker for that hit, but the save dice then needed to be rolled separately- if the marine died it would not have caused an extra blast marker for his death (in short, Disrupt lets you skip the 'save' step when placing blast markers).

In turn 3 you confused the end of turn rallying (remove half BMs) with the Regroup action (remove the highest of 2D6's worth of BMs). You got this right in every other turn, but it's an easy mistake to make- sometimes I still do!

Sorry that list ended up a bit long. I don't mean to slight your game playing at all- I know how many different games you play, and there are a lot of small, fiddly rules in Epic!

I look forward to your next report, and hope you'll go to 3000pts!

(just FYI- all of the above are core book rules, I'm not trying to corrupt you with community stuff )