The Power steering squeeling and "sucking" on full lock seems to be kinda "normal". I think everyones 155 does it (mine does).
The no oil pressure will be the sender unit probably or a bad connection at the sender, or broken wire, or..........
The tappety sound......does it do it all the time at idle, or just when cold ????
The 16v's suffer from gubbed variators which make it sound like a diesel at tickover, but it'll still sound like this when hot (I think).