Thanks for the kind words! 🙏
Is there a way after finishing a game to reset the sheets without manually removing all the damage/adding ammo so you can reuse?
Afraid not — the fastest route is to delete and pull a new sheet.
Is there an option to disable the app dice rolling, calculating damage without disabling the hit calculator, my groups/events insist on rolling real dice for everything, so we just need it to calculate hit numbers, assign heat and ammo use.
Yes-ish.
First, a sheet must support automations and automations must be enabled for the sheet to get the calc.
Second, the ••• menu contains granular automation options. (see
https://www.youtube.com/watch?v=VQ-peQjWv3c&t=112s .) Make sure damage-resolution related items you want to roll for are set to "Ask", as in "Ask for input". Not every event is in those setting but most are.
That'll get you what you described with your words. Though I smell more nuance in what your group is doing...
Just in case it's news, note that players can always declare shots at generic targets to get the benefits of auto heat and ammo tracking and then resolve the damage outcomes of by traditional roll, call, and mark. This should allow you to roll
everything at the cost of doing one set of chart lookups (hit location) and the defender having to mark damage groups manually (though with the benefit of auto damage transfer, crit-chance notice, flooding, etc.).
I had a mech take a second gyro hit, so the great big red DESTROYED came up, this however prevented me from returning fire in the same weapons phase as it did not allow me to select weapons, surely damage shouldn't take effect until you press the next phase button. This got me thinking (danger Will Robinson) about ammo explosions, I not a rules expert but doesn't ammo explosion happen after you have fired for this phase so I'm not sure the sheet takes that into account.
Here are three things you may be missing:
1. The rules as written are that players are to resolve all attack
to-hit checks before resolving any attack
damage 2. Flechs Sheets does not
require players to follow this strict sequence.
3. Moreover, Flechs Sheets accommodates/allows alternative 'folk' resolution sequencing as best it can (but its imperfect).
#1 is covered in the opening pages on weapon attack phase in most rulebooks if you want more details.
#2 is the case because it's literally not possible to enforce this sequence if Flechs is to work alongside paper sheets and also because alternative 'folk' attack resolution flows are very common and for good reasons. The later item is why there are no 'did all players resolve attack to-hit' pop-ups before applying damage like there are about incoming damage when leaving an attack phase.
Related to #3, you may have noticed that FS will allow you to declare and resolve a weapon attack even if that weapon was destroyed that phase. Plus it will not include modifiers (like a shoulder hit) from damage that same phase. This is technically not how the rules work but it is how players work. However, this fudging does hold true to cases of unit destruction or pilot incapacitation — and that's just the result of me prioritizing 'be clear about damage effects and their significance' over facilitating folk attack flows. 😬.
I can elaborate on the 'folk' flow phenomena if you'd like but it'll be a few words...
Lastly, you are correct that, generally speaking, attack damage induced ammo explosions
should happen after attack to-hit resolution as they are part of damage resolution sub-step. Just as with other damage effects, know that when using Flechs Sheets that is what happens if players follow the rules strictly, i.e. they resolve attack to hit before damage. If they are not, then they will need to hand wave things similar to how they do with paper sheets.
Are vehicles/infantry in the targeting scope, beyond the horizon or not in this galaxy of future possibilities! 
The project goals and road map is here:
https://quire.io/w/Flechs-sheets?share=gdj6amde2e6wmufi94nxb913b78djtOf note is the top level item: "Facilitate in-person on-the-table BattleTech gameplay, focused on novice-to-intermediate-level formats, i.e. 4v4 succession wars era biped mechs on standard terrain using rules from AGoAC boxed set or the BattleMech Manual."
That said, I am currently undertaking a re-write practically from the ground up, and it is just the case that Vehicles and standard Clan BattleArmor are in, but it will take such a long time that I'd humbly advise forgetting this sentence to avoid any disappointment.
