While in theory a smaller wheel could offer some strength advantages, in practice the wheel size for a MTB is pretty much irrelevant in this regard. Loads of people heavier than you run 29" wheels. Heck, even DH racing has mostly gone 29". This notion that 29" wheels would be weaker than 26" stuck around for years when 29ers first hit the scene. That is pretty much settled as a non-issue these days.
If you liked the feel of the 29" wheels, get 29" wheels. There are reasons for some people to go with 27.5" on some bikes (and I am not talking about how tall they are), but you would probably know if you were one of those people.
Here is some unsolicited opinion/advice: If your use for this is going to be primarily trail riding, you might look at some other offerings with more "modern MTB" geometry. The Marlin's geo is typical of what MTB hardtails were 12 years ago. For bikes that spend a bit of time on something other than singletrack, this is fine. It is a sensible compromise for a bike that spends a lot of time on roads (paved, dirt, gravel, commuting). But for primarily singletrack riding, geometry has improved dramatically in the past 5-7 years. Basically, modern MTB geo has gotten better for actual mountain biking, but less desirable for riding on roads (paved or otherwise). That's my take, anyway.
Is there a reason for Rock Shox in particular? Rock Shox makes a solid product at nearly all price levels from entry to top-tier, but there are other good options. Fox is also excellent, and offers high quality forks starting from affordable (this would be their Marzocchi branded stuff) to top tier. For my the reason I like RS forks is that they are relatively easy to rebuild, But if you don't do that stuff yourself, it is not really a selling point. Manitou is also making good stuff these days, though I don't often see them on stock builds. At the price point you are looking at, being brand-specific could really limit you option. Look at the model, not just the brand.