Hi RYR738
1-FL260 by NATEB is a standing agreement between two scottish sectors,Montrose(126.925) and Tay(124.5).The airspace around NATEB is extremely complex,this restriction gets you low enough to be under midlands group inbounds from the north east at FL270 and low enough that we have a fighting chance of jumping you with traffic climbing out of the Manchester and Scottish TMA's that routes via NATEB,when traffic permits then Montrose and Tay between them can cancel the restriction at NATEB but FL220 by OTBUN will still apply so that you remain clear of the Deancross sector which sits above the TMA.
2-The base of CAS at OTBUN is FL205,so you'll often find yourself levelling off at FL210 until passing there.It's badly designed as we would ideally like you lower so as to filter you into the TWEED hold at a reasonable level. It is the Otterburn danger D512/A that sits below the airway between NATEB and OTBUN,this prevents the base of the airway being lower.
3-Not annoying at all,the worst we can say is no! It involves a phonecall from the Talla controller to the Tay controller to ascertain whether they can accept you routeing that way, and what level of service that can be provided. It can be helpful,especially if you depart runway 06 to get you routeing direct as it keeps you from turning south towards the Tweed hold.However there can be a LOT of military activity outside CAS between Edinburgh and Newcastle,bear in mind that even under a deconfliction service that it's still up to you to see and avoid.
You're always welcome to come in and have a look round,cheers,rolaaand.