Awesomemod largely takes care of stuff that isn't even in Sims 2 anyway. With macrostatics and the other FFS hacks there isn't a lot left in Sims 2 that isn't covered by awesomeware.

Does Bodyshop work fine without Photoshop, and vice versa? If so, then check your Photoshop preferences. You can tell it how to use your system resources, such as where your 'scratch disc' is and how much memory to use. If Photoshop will not work at all then you need to troubleshoot that installation.

Try deleting your cache files. Are you saving on exit? Try saving before exit, if so.

I wouldn't advise to rezone to residential and then back to apartment; this can cause some problems. Instead it would be better to use the cheats:
boolProp aptBaseLotSpecificToolsDisabled false
boolProp aptSubLotSpecificToolsDisabled false
to make any changes. For the person not returning from work- forcing an error on all off/ on world objects will usually force a sim home, using the FFS Lotdebugger from MATY.

It's a coloured underlay for the water that gives it a 'reef' appearance . It seems to be shaped for Twikki, so it doesn't look good on other terrains. If you delete it then your Twikki Island water will look like ordinary hood water.

The screen turns blue- do you mean like a pale blue with the rotating hourglass going? If so then this sounds like a memory issue. I would advise to update graphics drivers, shutdown nonessential background tasks and reduce amount of CC to immediately help. For upgrading, more RAM or a more powerful graphics card could solve this, but it will depend upon your computer age and spec as to what is viable and economical.

May not be a hack conflict, but it could well be an out of date or incompatible hack. I'd suggest a binary search (50% method).

Hehe, I can imagine you ending up with hoods called Bognor Regis or Peckham! I use these:
http://nine.frenchboys.net/
http://www.seventhsanctum.com/index-name.php

It can bork the apartment controllers and cause glitchiness, such as invisible furnishings where they are meant to be visible. Pescado mentions it here:
http://www.moreawesomethanyou.com/smf/index.php/topic,14333.msg410486/topicseen.html#msg410486
There was another thread somewhere where he went into more detail, but I can't find it now. I wonder if rezoning is part of the problem with some of the Belladonna apartments too.

I wouldn't rezone- there seem to be problems caused by zoning a lot to apartment, then rezoning to residential and back to apartment again. I would scrap the lot and rebuild it if moving the sims out doesn't work.

Your folder may be correctly named, but did you also try the bodyshop trick? Generating a fresh folder usually helps (not sure if you tried that). Also, try removing your config folder from Documents/ EA Games/ The Sims 2 so that the game regenerates that, then re-enable CC and restart. No point in reinstalling, this is an issue with your userdata not your game data. I've seen this issue many times- if your objects are showing up but your bodyshop files aren't then it has to be a problem with your Downloads folder or your config file.

Try generating a fresh Downloads folder- it should be spelled with a capital D- Downloads. If it is called downloads then all items except CAS items will show up. If you still have an issue, try removing your Downloads folder then running Bodyshop so that the game generates the file for you. Then put your CC in there. If all this fails, then try disabling CC in game, then restarting, then re-enable and restart once more.

This is a tricky one- I've heard of cases where the beach portals are messed up by certain hacks or mods, so you could test without your custom content to check that. Creating a new vacation hood in a test hood and seeing if the beaches work there will tell you if it is a problem with your hood- also try creating a new hood without your downloads present, in cause it's being borked on hood creation. If all that fails, try reinstalling.

It could be a number of things- video as the previous poster mentioned, or perhaps hard drive. I would suggest to run a disc check anyway, as you've had some crashes.

Those cheats make the build tools available to use on the apartment after you have rented it, but they do not make the furniture appear. The furniture appears only if a townie rents the apartment, or if you shift-click the apartment door before renting (in debug mode) and choose 'rent furnished apartment'. Pescado's apartment hack allows you to rent a furnished apartment without debug being on- and also it corrects the exploit that you get the price of the rented furniture when you move out.
For noisy neighbours, you can click on their door to complain about the noise, or bang on the wall to make them stop.