Hi Holls
Glad to hear you have been busying yourself. They recommend you mix purees with milk if you need to thin them down - or at least they used to recommend this when I last prepared purees.
Yes, they can start having squash water, fruit juice and milk to 'drink' and it's best to establish this in a cup. That doesn't mean you have to get rid of bottles though. Certainly at first baby will still be having milk feeds through the day. You can move to a cup for them all if you want to. Don't worry if baby likes the comfort of a bottle though, it's fine for now.
Buying sippy cups:
I wish someone had explained the different types to me when I first started, so here goes.
There are free flow cups and no leak cups. Free flow cups are easier for baby to drink from - just turn upside down and drink drips out. Problem is baby will soon learn to 'sprinkle' and unless you want to spend half your time saying "no, don't do that!" they are not useful long term
No leak cups are more difficult to work though - child often has to either suck hard or bite down to 'open' the flow hole. Useful longer term to stop mess from sprinkling and cups being knocked over, but harder for little ones to work.
Another option is the straw lidded cup. These have an in-built straw so child drinks with beaker upright. They require a suck to get liquid to go up the straw but less difficult than no leak ones. Often leak less because of one-way valve in straw.
You can also get handles that convert your bottle into a beaker, but still with a teat. I don't think this is recommended for drinks other than milk or water though.
I know when we first started I ended up with a cupboard full of cups that we didn't like. So don't be like us and just think "we need to get a cup for the baby" and get the pretty one, or the brand name, or first one you see. Think through how the cup works and if it suits your child.