About over crowing: Look into pruning them.

About size and growth:
Once tomato fruits shows some color change, it is unlikely to grow any bigger. Then you can pick them and let them get full color on the counter (INdirect light). This is a good technique if the crack, birds pick at them, etc.
Of course, you can always let them get ripe on the vine.

If the tomatoes are red, they are ready. They won't grow any bigger! The orange ones will probably turn red, unless they are an orange variety (like Sungold). Enjoy!

Linda

Harvest those that are red or orange/red. Use snips so that you don't harm the stems.

If you keep the ripe ones harvested and the crop thinned a little, the remaining tomatoes are likely to be a bit larger.

Thanks, guys! Linda -- Yes, I have both red and orange varieties!

Well, we harvested the bright red and orange ones, but it turns out they did need to be riper. I'll have to figure out a good way to tell!

This has been established that once tomato turns color, the rest of ripening process is internal to the fruit and needs not any help from the mother plant.
A lot of gardeners harvest their tomatoes once color change occurs. They do this for several reasons :

--- rainy period ahead , to prevent spoilage. .
--- birds and other culprits eat/damage them.
--- Tomato variety is prone to splitting and cracking if left on vine long time.

After harvesting, just store them single layer on newspaper , AWAY from direct light, in room temperature.
If you be careful in picking and not blemishing them, those tomatoes can last for days if not weeks or until you consume them after changing full color.

I've heard the "collar" of the tomato dries up?

Aside from colo - Feel them. A ripe tomato has a totally different feel and hand weight from an unripe one. They are softer and heavier, have a 'give' to them when lightly squeezed between thumb and finger.

Dave