You will have to get a CPL before an ATPL. If you wanted a CPL now, then you would have to do the ATPL theory exams then a CPL flying course. You say you may want to be an instructor, at this point (on completion of CPL flying course) you could do an FI rating and work as a paid instructor. Now no doubt somebody will post and tell you that you don't need a CPL to instruct but you DO need one to get paid, so you really should do the CPL first.
Now, you also state that you may fancy a job in the corporate world, to do this you would need an Instrument Rating, once added to your CPL this licence is known as a CPL/IR. You will need to have the IR three years after your last ATPL exam pass to make sure your theory credits stay valid for ATPL issue. You may also hear the term Frozen ATPL, there is actually no such thing, this is just a term dreamt up by a flying training organisation to make a CPL/IR with ATPL theory credits sound better than it actually is. The ATPL licence issue comes later, at 1500 hours providing you meet the multi crew requirements etc
I imagine you are in a better position than most as you already have a bit of experience and exceed the minimum hours requirement to start any professional training course. I'm sure this along with your IMC rating will make things a little easier for you. I hope this helps, good luck.