Unfinished Maple 6 ft. L x 39 in. D x 1.5 in. T Butcher Block Island Countertop

It is one piece. It is very heavy so you may need help lifting it.

Maple never takes stain well.

This should work great for a darker stain. The birch will also work well. I would stay away from the beech, alder or acacia as those will want to yellow.

You can use which ever side appeals to you. All sides must be finished to prevent warping, as is true of any wood.

Chucky, As with most things, wood contracts and expands with temperature and changes in climate. Wood has "pores" which change based on what I just stated, effecting the process. In fact adjusting climate, is sometimes used to manipulate wood for specific results. So, the short answer is. Wood items should always be brought to room temperature before doing anything with them. Note However: If you leave your item at room temperature in a house with a very dry "climate," without sealing, you risk cracks and the stain will take differently then on a piece of wood with proper moisture content.

In my experience with this type of product there should be no concern with warping

It's wood. Of course you can stain it.

It's finger jointed hard maple.

Sam, Unless otherwise stated (water based) stain is an oil. If you were to oil ahead of staining this would effect the stains ability to penetrate. The water based should be obvious, "oil & water don't mix." As to the oil stain. Wood, like any other material can only take in so much moisture before reaching "saturation." If you oil first you have changed the amount of stain the wood can take in. If you use Mineral Oil, this will act as your finish, but it will dissipate and need to be reapplied as directed. If you choose to stain your top then you will also need to apply a sealer as stain is not "food safe" and could stain that nice new coat you lie on it. So, if you stain apply a polyurethane or other sealer which will "seal" the oil in and prevent drying. Hope this helps.

Of course you can join any two pieces of wood together but you'll need to know what you're doing. Cut both pieces for clean & straight edges, use joinery method of your choice to align them, and use whatever method of choice to join and hold them tight together. The joint will likely not be seamless because of the pattern - especially if joining end grain (short edges).