Hopefully picking up my '98 315R this week. I do know the fork seals need replacing although I'll probably spend some time trying to ride the thing before I tackle this job. Thinking ahead, I have some 7wt fork oil that I use on the Fox forks on my mountain bike - would this be OK to use or should I stump up for some 10wt?

Bear in mind that I'm realistically going to be using this bike for learning and big drops, etc are not really on the cards for the foreseeable future!

Yes it will be ok. Try it and the worst case is you have to swap it out again. ATF oil is roughly 8wt oil and a cheep way to go for fork oil if your aren't bothered with buying the premium stuff.