For a 6-6.5m £15-20k should get you a good condition 2nd hand one just out of warranty. Obviously a 6.5m wider beam slightly older.
Yes a 150hp on that size boat should be fine
Re layout, most boats these days are species by the original purchaser. So other than the med boats/mass produced Brig, ribeye, valiant etc the set up is random. They though generally are more leisure orientated in set up with some soft sun pads up front in the V and a bench at the rear.
Good brands include probably ribeye (slightly debated on here both ways), Humber, Osprey, ribquest, ribcraft, revenger, scorpion, delta, tornado amongst others.
Horses for courses though. Some are kitted out in a more utilitarian fashion than others, but as I say, one osprey to another could vary drastically in layout and appearance.
Rule of thumb, find a boat, if you like the layout, research the characteristics (on here), then if still happy, GET A SURVEY FOR THAT MONEY.