Actively losing weight-when do i go dress shopping ?

Dresses can take 4 to 8 months to come in, so that should be enough, but you can't take too long to decide. Order for the size you are then, not your goal weight, because it's much easier to alter a dress smaller than try and make it bigger.

You need to leave enough time for them to make the dress and have it come in but you don't want to keep losing weight and have to have major alterations done. Could you wait a little longer and buy a dress off the rack or just order a smaller size when you order your dress?

It’s typically recommended to start dress shopping one year out, as most people have to go to several different shops before finding “the one”. A lot of it will depend on what designer you choose – some designers will have a 4-6 month turn around time, while others can have 8-12 months. You want to make sure you also leave yourself plenty of room for alterations (I was told at least 4-6 weeks), and also don’t want to cut it super close, as dresses sometimes come in with errors (wrong size, wrong color, wrong dress, etc.), and there have also been a lot of shipping delays from overseas lately.
If you want to wait as long as possible, I would consider purchasing a sample gown off the rack, or even a secondhand wedding dress from one of the many websites that cater to such things. You could also speak to the salesperson helping you, and request that they pull dresses that can easily be altered down (because not all dresses can be!). Corset backs are a great option when losing weight, because you can let them out or cinch them down a size or 2 without any alterations being done.

I'm in the same boat. I'm looking now, and if I find a dress I like, I'll buy it for my current size. It can always be taken it, but not so easily let out if you don't lose as much as you think you will.