Hemming your Gustin's

I hem my normal weight Gustins at a local tailor. Nothing crazy regular hem. $7.

Super heavies, beasts, and super lights I haven't hemmed. I won't hem my samurai's since they are short enough to stack and not look stupid.

I get my jeans chainstitched. you have to remember that most small companies producing selvedge denim always produce jeans with long inseams. I think this is more about efficiency than anything. With longer inseams, you the customer, gets to decide the length rather than relying on Brand X to do it for you. If I was 6'5 then I might not need hemming, but at 5'11 I do.

It Is. But if you cheep out it may bug you over the life of the jeans.
If your double cuffing, no worries.
But a single or no cuff, get it done right.
The fact that you bought selvege says that you appreciate/like/want/etc something a little more different/better/interesting/etc over the other mall jeans.
Don't finish it off with what they come with. Get the chain stitch.

They're also one of the best makers of jeans outside of Japan (and they very much hold their own against the likes of Iron Heart - seriously)

If you send to Railcar, how do you tell them how long you want them to be? Do you try them on at home and cuff to where you want it? Or do you tell them you want it to be a 32 long or something?

When you place your order on line it will ask you what you want (1/2" intervals). So the length will be on your order forum. I also put a copy of the order with the length highlighted.
You can also change the color of the thread (put the color you want in the notes) If you want to keep the red Gustin, there's no need to put anything. They put the same.
It is a pain. And cost. But it's right.

there are several companies that offer chainstitching services, each with their own pricing. I got mine done for free through Blue Owl Workshop, but it was only free because I bought jeans from them. there are other companies like abfits.com and railcarfinegoods which has been mentioned, but I have no experience with these companies. It appears abfits.com charges $15 for chainstitching services but BOW and Railcar charge $25.

knowing your inseam is important. You should measure the inseam on your best fitting jeans and go with that. If I get jeans hemmed/chainstitched I first determine whether or not i'll cuff, and this is dependent on the size of the cuff opening and the type of pants (selvedge jeans vs chinos). typically if the cuff opening measures 8-8.25" across then i'll cuff and go with a longer inseam, and if it's below 8", like 7.75" then i won't cuff and i'll have the inseam a little shorter. I have a pair of N&F chinos that I plan on having hemmed/chainstitched, but because they're chinos I'll probably go with a shorter length (since I won't be cuffing them). YMMV

Honestly from a distance can you really tell the difference? Chainstitching is weaker as well. You like Gustin for flat felled seams already doesn't it make sense to have a lock stitch hem too?

I just hem with normal straight seem on my singer. I do buy extra strong and thick thread tho and have copper, black, navy, grey and offwhite. Been learning to make pretty solid bar tack but cant do it over the thickest part, but still like to do it. I dont think anyone under normal wearing notice the difference on my hemming vs chainstitch.

I usually Just hem them straight away but make them half an inch to an inch extra to acommodate for washing in a years time.

Ok I'm just going to go to the dry cleaners today and ask them if they tailor jeans. Is there a certain type of hem I need to ask for? I like the idea of sticking with dark blue or black thread.

I would ask for a standard stitch or lock stitch. I would advise against an "original hem" which cuts off the hem and re attached the original chain stitch.