I would recommend doing longer trips offshore in the company of other boats, it is far safer and you can learn a lot from others, get a tow if required etc.
Regarding the SIB and engine, I would probably consider a min. 4m boat with a modern 4 stroke outboard. They are very fuel efficient and quieter for longer trips. A SIB is a very seaworthy boat but you will not be able to maintain a high speed comfortably and safely in anything other than calm seas. Long rolling swells are better than short, steep chop.
I have done some very long coastal trips in 4m+ SIBs packed with a lot of camping gear. Everything must be stowed securely... we used a cargo net combined with waterproof bags which worked very well. We carried separate 25l fuel tanks to extend the range.
Going further offshore is another matter and it needs proper preparation and planning. Keep in mind your distance from a safe haven should your engine fail, the weather get worse than forecast etc.