Hey, I'll second the previous post. There's a lot of great info on sprinter-source.com. I'm working on porting over our build thread from there to here to reach more people.
Click here if you want to check it out in the meantime. Our build is finished now, but we certainly had a overlanding slant throughout our build. We've done some mild off-roading and things have been working great.
My advice on options with specific regard to what you've outlined is to get all the things you're on the fence about, if your budget allows.
1. The exterior lighting package is great to have if you've wandered away from camp in the middle of the desert at night. Click the unlock button, and the van will shine light all around itself for you, highlighting any hazards along your walk back home.
2. The electric sliding door is great. Kinda. We didn't want it either, but it was already installed on the van we found, so we accepted it. Let me explain -
sometimes it has issues. Not often, but once in a while it doesn't like to latch properly. It's a minor nuisance. BUT, the doors heavy. And with a 4WD van, it's also high. And if you're considering a lift and/or taller tires, the handle gets even higher. It is an awkward shoulder movement, that has the potential for an injury if you're not careful. Having been on the fence about the sliding door, we're very happy that we ended up with it, even considering it's intermittent issues. They're pretty rare. Maybe every few weeks, with daily-van-living?
3. The auxiliary battery got zero usage from us. BUT! I was pumped to have the OEM battery tray. By modifying it slightly, I was able to fit a 170Ah lithium battery in the same space. Having the battery tray for the original battery saved me a bunch of time, and I think we ended up with a nicer finished product because of it. I disconnected the charge wire under the driver's seat to completely isolate the house side batteries from the van side. If you want to keep the systems linked, the already-installed wiring is even more reason to get this option.
4. Wood floor with D-rings. The only thing worthless is the D-rings, really. You could theoretically use them to tie down...something...in your build. I don't know what that may be. For us, it was nothing. And most of them went in the trash. BUT! (Lots of big BUTs in here, don't judge me) the wood floor saved me a ton of time. You could buy and cut your own after tracing the contour of the floor, the result would be nearly the same. The wood floor has a plastic coating on the top face that seems super durable, so that's a bonus I wouldn't have been able to replicate very well. We ultimately raised our floor about 1-1/4" to insulate beneath it, and I just screwed the wood floor down to the joists I installed underneath it. It was a big time saver, and a pretty nice piece. I'd recommend it.
Hopefully that helps you some. If you want to know about other options, let me know. We didn't care for the rear step thing, it wasn't on our list of nice-to-haves when we were considering specing our own van, but it came on the one we ended up with and we really like it. I can't think of any other options like this right now, but I know there were a couple other things. My main point is, if you can find something that checks your boxes, don't sweat the additional items, because you learn to enjoy them pretty quickly.
