He seems fine. Each baby is different in amounts they eat.
Don't give him juice... especially anything "citrus"... until AFTER 1 years old. It's allergenic. Introducing it too early may trigger allergies. Same for other "off limit" foods at this age.
You should also really check with your Pediatrician.
They don't "need" juice yet.. it is just sugar.
If you want to introduce another "liquid", then do water.
Water and/or breastmilk/his formula is MORE than enough.
Remember that breastmilk/formula is the PRIMARY source of nutrition for a baby in their first year of life. Baby should not be "weaned" from either one yet.
My Pediatrician said, give breastmilk/formula FIRST...BEFORE solids. But, if you are wanting to "wean" the baby, THEN you give solids first. It's a priority that you "choose." Some Moms like to concentrate on giving solids... and lessening the breast/formula intake....other's dont. Me, I always nursed/gave a bottle to my kids first... then, solids. And nursed before each nap and sleep time, and after they woke up, and on demand at other times.
You rotate foods according to "introducing" them, one at a time. THEN if you know there is no allergenic reaction to it after a few days, THEN you can "introduce" another food.
At 6 months of age, you are acclimating the baby to gradually working up to 3 meals per day. There is no rush. At this age anyway, they still need their breast/formula intake.
As for amounts eaten... every baby will eat varying amounts, and like an adult, their appetites vary too. I REALLY recommend that you not "compare" how much your son eats to others... he does NOT have to eat the same amounts. Each baby is different. I have seen some Moms trying to get their baby to eat an entire jar of food... and clearly the baby didn't want too. But the Mom "thought" they "had to" eat the whole jar because of the erroneous idea that a "jar" was a "serving" and then they wondered "why" their baby was hard to feed.
As for how much your baby should be eating and "cues"... a baby will keep opening their mouth if they are still hungry... if they turn away or clamp their mouth shut, or push your hand away...then they don't want anymore and are full.
At this age, "serving amounts" ARE in terms of tablespoons. Your son seems to be doing fine. There is NO RUSH to get the baby to eat a "buffet" of food all day. They can have little snacks here and there...but again, not so it interferes with the breastmilk intake etc. Some babies eat all at one sitting.. and others are "grazers." Meaning, they eat small amounts throughout the day. Each baby is different. My eldest for example, ate tons at each sitting. Then she was fine. My youngest on the other hand.. is a grazer...he eats LITTLE amounts per sitting... then he's satisfied...they he grazes here and there during the day only if he is hungry.
As for "schedules" this is what I did: I nursed before each naptime/sleep time & after each time they woke up. I also nursed before any "solids" meal. And on demand other than that.
There are so many different "schedules." Just see what works out best for baby and you. But, regularity is best, to get them on a routine.
Good luck,
S.