ARLINGTON -- The Rangers are preparing to defend their 2015 American League West title with close to the same team that lost to the Blue Jays in the AL Division Series.

There are still over six weeks left in the offseason, but to this point the Rangers have been one of the least active teams this winter. They were able to re-sign starter Colby Lewis, trade for reliever Tom Wilhelmsen, outfielder James Jones and infielder Patrick Kivlehan from the Mariners and sign reliever Tony Barnette out of Japan. In their pursuit of a right-handed hitter, they also signed outfielder Justin Ruggiano.

:: 2015 Year in Review | 2016 Outlook ::

But unless something transpires in the waning weeks of the winter, the Rangers have pretty much decided what worked in 2015 can again in 2016. It might get even better if certain things fall their way, but there is also a possibility the Rangers could reverse course again.

The Rangers have a productive farm system, but they also have a group of core players that is getting older and continually dealing with physical issues. There are a wide variety of variables facing the Rangers as they prepare for next season.

Here are five things to watch:

1. Can the Big Four stay healthy and produce?

Adrian Beltre, Josh Hamilton, Prince Fielder and Shin-Soo Choo have combined to appear in 15 All-Star Games. However, all four are 30-something and have missed significant time at some point in the past two years. All four have also required at least one surgical procedure in that time.

Fielder was the AL Comeback Player of the Year in 2015 and Choo had a tremendous second half. So did Beltre, despite a sprained left thumb that required surgery after the season.

The challenge is keeping them all healthy and on the field. Beltre will be 37 next season, and in the final year of his contract. Hamilton will be 35 in May, and staying on the field has always been a challenge for him.

Video: Fielder earns Bounceback Player honors

2. Will Darvish be able to boost the rotation?

Yu Darvish is scheduled to return from Tommy John surgery in either May or June. The actual date is far from set, and it is still unknown at what level Darvish will be at when he does return.

That leaves Cole Hamels, Derek Holland, Martin Perez and Lewis with spots in the rotation. As of now, Nick Martinez, Chi Chi Gonzalez and Anthony Ranaudo are in line to compete for the fifth spot. The Rangers have high expectations for Darvish upon his return, but they are still looking for more starting depth.

3. What's up down the middle?

The Rangers return Delino DeShields to play center, and they have Robinson Chirinos and Chris Gimenez back at catcher. The Rangers have spoken of potential upgrades at both positions.

But so far they have added only Jones, a left-handed hitter, as an alternative to DeShields in center. As for catcher, the Rangers made a run in trade talks for a couple of young catchers at the Winter Meetings, but came up empty. They also re-signed Bobby Wilson to a Minor League deal because of his defensive aptitude.

Video: [email protected] Gm5: DeShields starts things with a double

DeShields was more than the Rangers had hoped for as a Rule 5 Draft pick, taking over in center field and at leadoff for Leonys Martin. Chirinos showed he could be a front-line catcher before missing the final two months because of a shoulder surgery, and Gimenez played well in his absence.

The Rangers could be set at both positions, but it is clear they are still hoping to add more depth.

4. How will the coaching changes impact the Rangers?

The Rangers made significant coaching changes after the season as Mike Maddux (pitching coach), Andy Hawkins (bullpen) and Dave Magadan (hitting) all left the organization. Assistant hitting coach Bobby Jones was reassigned.

Video: Daniels, Banister on hiring of Brocail and Iapoce

Doug Brocail was hired away from the Astros to be the pitching coach, and Brad Holman was promoted from Triple-A to be the bullpen coach. Both are highly regarded for working with young pitchers, but will now be dealing with a veteran staff.

New hitting coach Anthony Iapoce has never worked at the big league level, nor has assistant hitting coach Justin Mashore, who was promoted from Triple-A. Mashore and Holman both have experience working with the Rangers' prospects, but a complete change in the hitting and pitching instruction bears watching.

5. What will happen to Joey Gallo?

Beltre's sprained thumb forced the Rangers to promote Gallo to the big leagues ahead of the planned timetable. The Rangers' deluxe power prodigy showed flashes of his ability but overall struggled at the highest level.

The plan is for Gallo to get more time at Triple-A and hope his premature promotion hasn't led to a permanent setback.

Video: [email protected]: Gallo launches the Rangers' fourth home run