hi zebra, sorry I didn't reply to your previous thread, I did see it but because I'm not a SALT thought it was better to leave it to a professional.
background - at 3 DS was severely delayed with language and receptive, around 12-18 months behind with both. He had lots of single words (say 100-150) and the odd phrase. More worrying he had lots of "telly talk" - rote repetition of TV scripts. He has never had any speech sound problems.
I've done group therapy with DS, and have found it pretty good, it's been 2 or 3 SALTs with there being 3 to 6 kids in the group. One advantage of group therapy is that they focus on skills kids need in school/nursery, like turn taking and sitting and listening. So although I think 1-1 is slightly better, the groups aren't bad at all.
re:bilingualism. no personal experience, but what I've read on the internet (and what Moondog who is a SALT who sometimes posts here) says is that it doesn't cause problems, and you should carry on using both languages.
PECs - not too late at all! I was very unwilling to use PECs as I felt it was a step backwards as DS had lots of single words and the odd phrase, but I am soooo glad I did start using them - private SLT put together a communication book to get DS saying things like "I" + "want" + "more" + "juice", and then that springboarded on to him being able to generate sentences easily himself, it really made something click in his mind. the other important piece of advice from private SLT was that verbs are the building blocks of sentences, so I had to focus on teaching DS more verbs rather than nouns.