Regarding the bus...
There's absolutely no way to deploy ground spoilers manually on A320!! One can only arm them and wait for automatics to their work once the activation conditions are met. Manual deployment some PPRuNers wrote about would only deploys spoilers 2,3 and 4 in speedbrake mode and that only if config full (i.e. maximum extension of flaps and slats) was not used for landing. Ergo, this (hypothetical) procedure is unapproved, potentially hazardous and spectacularly ineffective.
In landing phase, if spoilers are armed, they will deploy as soon as both main gears have touched down and both thrust levers are at idle. If they are not armed, they will deploy when at least one thrust lever is moved to reverse but other one has to be at idle or below. Also there's partial extension mode when only one main gear strut is compressed and reverse is selected - it leads to compression of other strut and therefore to full extension. Allegedly this mode was introduced after Warsaw accident and because if it, my company SOP is to always select at least idle reverse.
Christmas trees on wheel and f/ctl pages are not analog indicators - they don't show the angle of deployment of the related spoiler - only if it's out more than 2.5°.
Apart from reverse detent, all other detents on A320 TLs are "soft", pilots need only to apply small to moderate force to move levers out of or through them.
MAX autobrake is RTO mode only because there's would be no delay between touchdown and full brake application. Main risk here is not overheated brakes, but smashing the nosewheel into tarmac and possibly moving NLG assembly into cockpit. For maximum stopping performance procedure is to touchdown, select reverse simultaneously with settling the nosewheel on the runway and use maximum manual braking.
Only time when thrust cannot be controlled by thrust levers is when TOGA LK is activated but to activate TOGA LK you have to fly way below VLS (airbusspeak for Vref) - not very likely to have happened here.
There are two pick-off units for each thrust lever angle. Failure of one has no major effect on thrust control. However if their measured angles disagree or they both fail, FADEC automatically selects idle thrust when airplane is on the ground.
Provided it wasn't disconnected by bringing thrust levers to idle during flare, autothrust automatically disengages on ground after landing and it cannot remain in speed mode. Possible complications of landing with thrust levers out of idle are a) engines trying to match TL demand or b) getting THR LK - engines maintaining last ATHR commanded thrust while the TLs are in CLB detent. During autoland ATHR will comand idle thrust, I'm not sure about its behaviour during manual landing as it's against my company's SOP to use ATHR while flying manually.