I would think your “room with a view” theory is as likely to be a member of staff as a guest. As in my opinion, if it was an abduction scenario then the MOST likely reason to open a shutter that was not used to either enter or exit, may have been to detract from it looking like an “inside job” , i.e. use of a key. (Like Sadie I don't believe the sliding door was used - too many stairs, too much light etc.) 
When you say "member of staff as a guest" do you mean a staff member that was staying in one of the holiday apartments? But by the McCanns own admission the patio door was left unlocked so no key required. Experts in the following docu visited PDL and the apartment at night. You can see how dark the steps are leading down to road; then take a couple of steps on the footpath, along the alley and up another alley between the two blocks which takes you into the car park. What could be easier?!
https://www.youtube.com/watch?v=khP0dEsZaug - watch 14 mins in to 18 mins. Watch the full 4 mins.
I personally believe that in an abduction scenario there was more than one perp - but at least one of them worked at the Ocean Club. (The wages that some of them mention seem very low…so I guess if there was the possibility of financial gain, it may have been hard to resist - especially if you were mainly a look out person etc.).
Yes you may be right there may well have been more than one perp either same sex or different. I would not rule out a woman being involved. I would also not rule out some seemingly nice middle class person(s) staying in an attractive looking apartment either. The fact workers at OC may have been low paid might or might not be a feature. There are millions of low paid workers all over the globe and most don't resort to child abduction.
This could also explain also why the keys for block 5 supposedly mysteriously disappeared from the maintenance department for at least a period of time during that particular week. (This was reported in the media years later, which was also odd because they were supposedly under lock and key in a safe that could only be accessed by maintenance workers).
I've seen in other cases there are always red herrings. Did anyone check with maintenance whether or not any work was carried out on any of the apartments in block 5?
Additionally, on the Wednesday evening Rachel Oldfield was home ill directly next door to 5A. She heard no crying….so Madeleine may have been confused about which night she had actually woken. (That being the case, then the two evenings noted for disturbances i.e. Tuesday and Thursday, would have been on two of the nights that the entirety of the Tapas group were together at dinner. I think the only other night was Monday, but that was also the first time in the holiday that they had all dined together, without the children as the Sunday night Matt Oldfield was ill).
I read RO's WS but don't recall her saying she stayed in on the Wed eve but I'm new to the case any you probably no more of the detail than I do. Assuming RO was in maybe she was asleep? Mrs Fenn heard MM crying on 1st and MM said to KM on Thu why didn't you come when Shaun and I were crying so that's Tue and Wed eve not Tue and Thu eve?
Talking of Matt, his check on 3rd May bugs me not just because he said the door was ajar but because his wife claimed in one of her statements that her husband had checked the parents room to see if M was sleeping there. Matt does not mention this in his statement. He claims that the door was ajar, that he didn’t enter the room but observed both twins and that he was distracted by books on his way out. However, due to the nature of the fabric surrounding the travel cots - he would only have seen both twins if he came further into the room, than he seems to have remembered. So I believe that if his wife’s statement is correct - I can only imagine that some part of his subconscious may have clocked that M was not in the room....but maybe after checking the parents room - he became temporarily distracted by the books and left without re-checking. If that is the case, in all likelihood he would have been embarrassed directly after the abduction and possibly adjusted his recollection accordingly.
Again I don't recall reading in RO's ws that MO checked in McCanns room. I thought MO acknowledged that he did not physically observe MM from his vantage point which was limited to the twins?
If that was the case, it could mean there was only a 20 minute abduction window between 21.10 and 21.30.
How long do you think it would take to enter the unlocked patio door and leave with MM? She may well have had tape put across her mouth and then bundled into a sports holdall or small suitcase.
There is also one other statement that really bugs me - Neil Berry claims a girl helped him and Raj erect a cot some time between 19.00 and 20:00 on 3rd May. Neil claimed her boyfriend worked for the maintenance dept and was called “Rob”. Yet there is no maintenance man called Rob - in fact I don’t think any member of staff was called Rob. (Neil may have remember the name incorrectly). However, from the other statements I can only find two maintenance workers who mention girlfriends that worked at the complex - Tiago and Nuno (Hayley May Crawford was Nuno's boyfriend - not sure who Tiago’s girlfriend was).
Anyway, Hayley’s statement does not fit with Neil's timeline and Tiago says he stayed at his girlfriend’s house in Burgau that night - and that they both learned about the abduction on their way to work the following day. Yet the other maintenance worker Miguel says that on 3rd May at 18.20 he travelled in the company of Tiago to Burgau. (He does not mention Tiago's girlfriend, so I am not sure if she was still working or already at home).
If the girl Neil Berry talks about was on duty between 19.00 and 20.00, I can only assume she was likely doing a late shift and would have learned about the abduction - yet from what I can see from the maintenance workers, only Nuno (someone called him looking for a torch) and Silvia Batista’s husband admit to learning about the incident on the actual night - the other maintenance workers seemed to learned about it the following morning - mostly I think from the head of maintenance). Anyhow, maybe its a "nothing burger"…..but it annoys me that I can’t work out who the girl is!
I've no idea about any of the above. As I said I'm new to the case so can only look at the big picture at the moment not the detail which may well be where the answers are!
