I have used semi synthetic oil in my bikes before and all was fine. I know we've all heard stories of slipping clutches but as far as I am aware these were mainly to do with fully synthetic oils (cue many replies...)
You can always try the oil you've already got, as it's in a sealed container it will still be good, if you get clutch slip just drain it out.
I've always used HiFlo filters, never had a problem.
Before going into Halfords with your trade card just have a look around a few other places as Halfords might not be the cheapest. Tesco had a fantastic offer on a while ago...
Shell Rotella T6 picked up an MA rating a few years back because Shell saw an opportunity to sell their diesel lorry oil to motorcyclists and submitted it for testing. The formula was not changed.
I used Morris Ringfree oil in my FJ1200 for years. It is essentially a 'lorry oil'. Morris also produce some bike specific oils which happen to be more expensive but the Morris salesman said it was the same stuff with a more expensive label on the tin.
The best tip I've ever been given regarding oil is... If you need it now then get it, if you see it on offer at say £4 off and it's a genuine offer then get some because you'll need it sooner or later.