What would you do? what would you use? How long you think it would take you?
Let's collaborate a little. This isn't about making money, this is about restoring this to its rightful state.
I have done more than 1 labor of love project, and always better for it...but never financially. Let me first establish a foundation to terms. In my reality, to restore correctly, is what is done to museum pieces.
With full respect to you, and I believe you are 100% sincere, but honesty and integrity are not equated with ability. A pastor may be a moral guy, but this does not mean he has skillss. The questions you asked indicate you are in way over your head to restore to my definition of "rightful state". There is a huge gap between making something look nice.....and professional restoration. I suspicion you are just trying to make it look better, not restore it, and nothing wrong with that. Just as you are doing, I also have done many a project to improve. Please read the following comments with this in mind, and apply to what fits best for you.
Previous stripping info provided by others is sound. Heavy water is always a bad idea, but this bench is so far gone, you could hardly make it worse, no matter the stripper used. I agree, upon completion get it neutralized/clean
and dry before moving forward. This could mean a day, or days, but is never minutes. (note the black...that is what water does to many open grain woods as this one has). My most common mistake in refinishing is rushing dry times.....you can't beat experience. You can use wood bleach, but you will not remove all dark staining, so don't kill yourself trying. Be thorough, and realistic to result. I always start with weak chemical, and go progressively stronger as needed. Denatured alcohol will strip shellac. IMO there is no stain used prior, but rather existing coloring being the result of ambering from product age. Even with sand after strip, which I do recommend, you will not get the wood looking like new. Improve is the operative word. Personally I do not like the suggestion of a clear, because to my trained eye, with clear only, I will immediately notice the previous damage, but if that is the "patina" the customer likes....that is what you give them. Define your finished result and proceed with a system accordingly. At minimum I would use a pigmented clear as done by use of a dye stain, but I think this not the project for you to experiment with this type. A grain filler is a good idea to hide the black that will remain in the open grain if customer prefers no colorant to the surface grain. The water borne finishes, almost with every MFR, will not amber over time. I think gel stains are the "cats meow" for refinishing, having greater ability to hide blemishes with less effort. My #1 recommendation to you is a gel stain, giving you the best odds of a satisfied customer.
As I do not know your definition of restore, the same exists with you and your customer. Therefore I recommend a sample to establish a definition, and have them sign off. This alone can take hours and hours, but it only takes getting burned 1 time because of an assumption, and you will never do it again.
What has not been talked about, is the glaring water damage evident to the structure. 20% of my work is painting trade related, another 60% carpenter/cabinetmaker. To refinish and not remedy the wood damage and assembly failure, is not to IMO restoring to its rightful state. So IMO you first need a cabinetmaker. Not only do joints need glue/clamping, pics indicate some pieces of trim need to be replicated by a millwork shop, as old has shrunk so bad, no refinisher exists who can close the open joints as shown on floor miters.
As to type of finished clear product, because this piece appears to be stored outdoors on a covered porch, this means you need a product with greater flexibility, possibly even good UV resistance. Just this week I used some General Finishes 450 with great results to application performance....cannot testify to longevity. However with greater flexibility of an exterior product (paint or varnish) means the surface is softer....so prioritize type accordingly. Remember lots of light coats just heavy enough to level off....not 2 thick ones.
2 years ago, a contributor on PT told me about Woodweb.com, because more furniture refinishers found there. As with the many master painters on this site who I look up to, there are many master furniture finishers on that. You would need 25 years of industry specific experience to even begin to talk apples to apples with them, as is true with the masters on paint talk. Each guy has a favorite product, there is no such thing as best MFR, it gets super technical, and
is all about a tried and proven system, that
only time and experience makes one able to replicate. For example, it is like comparing the best athlete in the world at a specific sport, to a high school freshman.....some things just cannot be learned in a week no matter how sincere and gifted you are. For furniture grade finishes, you must have a spray booth....the technical difference between a fine furniture finish and what a "field painter" accomplishes is enormous....it all depends upon your definition to terms....on how close you look....and most importantly how close your customer will look and what they expect. As a word of advice....on any of these web sites....be very careful about using the word
best.....that is Pandora's box...I am never ceased to be amazed after 31 years in the industry...that a guy can never stop learning....stay humble...lots of tried and true experience is shared here....and for FREE.
If a museum type of restoration is priority, IMO you are disrespecting your customer to take this on. Any seasoned PRO will do it better and for a lower cost. If "improved" is what is acceptable, hours till completion are relative to your definition of restoration.
Hope this helps, and wish you the best.