At 6mo it is really about getting used to taste and texture. I really wouldn't worry about it in any way. If he doesn't take to something offer it again later & see.
Also no reason not to mix foods together, I mean if you look at most foods we eat they are multiple flavours. I used to do apple & Zucchini, lentil & carrot & things like that - they both stopped eating it at later ages though LOL
Honestly I was saying to my 11yo the other day, he was such a good eater at 1yo & now he is so inconsistent, he likes prawns in a carbonara sauce, but I do a garlic sauce - which was really just the same thing with a little garlic & serve it with rice rather than pasta & he says he doesn't like it.
Honestly take it as it comes, from a BTDT the more you worry about food the bigger the issues you will have.