I've gone back to work when each of my 3 were 6 months old (full time with DC1, 4 days a week with DCs 2 and 3) and it was fairly straightforward.
I expressed a couple of times a day for the first couple of weeks but that is more to do with comfort than needing a supply of milk. After that it was one express per day 15-30mins to get enough milk for the next day and maybe a couple of spare oz. DS1 and DD would take 3-4oz spread over the day. DS2 drank more, probably 6-7oz but he wasn't bothered if I sometimes sent him with a bit less. The rest of the time they would drink water. None of them had bottles just a bog standard sippy cup.
Feeding the rest of the time was on demand, like it always had been although the first thing I did when I got home was to give them a big feed.
Don't worry if he doesn't do a lot of solids. DS1 ate barely anything til 7.5 months and he was fine. He just adjusted his feeding pattern to when I was around.
My tips would be- get a good electric double pump. I eventually got the medela double and it was fab, made expressing much quicker. If you find it difficult to get let down with a pump then take a picture of your baby in to work to look at while you express- it really makes a difference. I just washed everything in really hot water rather than faff on with a steriliser. Milk went in a little cool bag in the fridge. I did have to teach nursery that they didn't have to throw the milk away if they didn't accept it first time round or only had a little and that it was fine to put it back in the fridge for later.
I stopped expressing at about 9 months for DS1 and DD. DS2 I went up to 11 months as he drank more than the others did. The older children self weaned at 20 and 21 months while DS2 is still going strong at 16months.
Good luck- it really isn't as difficult in practice as it seems in theory. Kellymom really helped me when I was planning with DS1- lots of tips on there.