I think you're being over-cautious tbh,
Jarvis was let off lead young, and has attempted to approach every dog he's ever met since then
his recall is something we practise on every walk, and it is generally very good, he's a fairly typical cocker in that he has his moments when it'll take a few calls to get him back, but he always comes because we practise so much.
With regards to meeting other dogs, Jarvis has met hundreds, and because he has practised his social skills so much he knows who to approach and who not to
in all his time he has only ever had one attack which was a real attack as such, and that was from an in-season bitch, so just down to hormones rather than an aggressive dog iykwim. Lots of dogs do get gobby with others when on lead (Jarvis included
) and it's an important part of their socialising IMO. the long line is a useful training tool, but it is just that, to be used for training, not an alternative to a recall.
