Hello,
it seems, from our own experiences and from what I have heard, that agencies/LAs all do it a bit differently. E.g. ours, we expressed interest in FtA; and explored ramifications during assessment. But we were only approved to adopt. When a possible FtA link came up/was suggested to us, nothing happened for a while, until everything was 'certain' (as certain as it gets); then we were approved to foster a named child (rather than just generally approved to foster). Introductions started the very next day. (Meaning, they left the approval very late, and then had to get it ratified super quickly. Also meaning, we didn't know until the day before we met DC if this was actually going to happen. Makes it hard to organise things like taking leave. Remember, as things stand right now, you don't get adoption leave before the placement changes into an adoption placement). We didn't have any specific training for the fostering part, just a quick sit-down with the manager of the fostering team to discuss the LA's regulations regarding fostering, and which ones did/didn't apply to us. E.g. we were not required to write a 'safer caring policy' despite all FCs in this LA needing to have such a policy. But we were required e.g. to write weekly reports.
I gather that in some LAs, you will only be approved to adopt, but if a possible FtA link comes up, you will quickly be approved to foster as well, and perhaps sent on a 'skills to foster' course (or parts of it) while you're waiting for the match to become certain.
And yet in other agencies, you will be approved simultaneously to foster and to adopt. Sometimes you will have been sent on fostering training days as well as the adoption prep course; sometimes, the specific fostering issues are just discussed during home study.
So in your circumstances, I suspect it's an issue of letting your SW know that you are potentially interested (you can still say yes/no on a case by case basis). Then take it from there. When (if) you let your SW know, you can also use the opportunity to inquire if, how and when you would be approved/trained for fostering. (Chances are your SW won't know exactly either, and will have to check with their managers first).
I believe it is pretty unusual to have a FtA placement with a child not from your own LA (the LA that approved you, that is). Because a LA that has a child who would be suitable for FtA, but no FtA adopters available, will just keep that child in regular foster care until they can start looking for 'proper' adopters, rather than looking for FtA adopters elsewhere/outside of the LA. So IMO there is not much point in letting other LAs know. Can't say if you are 'allowed' - our LA asked us not to pursue 'outside' links for at least three months after approval, I assume yours probably has a similar policy.
What I would say though is this: FtA can be a great thing. However, it is not for the faint-hearted. I would not advise you to agree to FtA before having explored it very carefully. Some SWs like to make out as if it were basically the same thing as regular adoption, just a bit sooner, with no downsides/risks. The reality is (can be) quite different!