I would like to see the Astros make a run at Alex Gordon. 350 OB% and some of the best defense in the league. Alex in left, Gomez in center and Springer in right would save a LOT of runs and Gordon could plug into third base as needed as well. He was a pretty good defensive third baseman, although he is a great defensive left fielder. Offer him Sandoval's deal and see how much higher you have to go. I would go 6/100 on him all day long.
I would turn first over to Reed. Dude is ready even if he struggles a bit.
Third is a problem with no real options.
Castro is just so good defensively that he makes up for the horrible bat.
Gattis is fine as a DH so long as he bats 6th or 7th and not 4th.
So then you could run out...
Altuve
Gordon
Correa
Springer
Gomez
Gattis
Reed
Valbuena
Castro
That is a stout lineup offensively and defensively. Have Lowrie, Marwin, Stassi, Tucker and/or Rasmus (depends on price) on the bench and that is a strong bench. Gotta get rid of the Korean. He hits a little but he is simply not a MLB catcher defensively and he clogs the base paths so bad.
Pitching you have 3 bad a$$e$ in Keuchel, McCullers, and McHugh. Mccullers got robbed of so many wins by the bullpen and offense. Neither helped him any last year. Fiers is fine as a 4th or 5th guy and I would bring up Appel to battle VVelasquez for the final spot. I know Appel hasn't done it enough, but he is mature enough and he just needs to see if he can do it or not. Bullpen is a disaster of course, need someone who can get over 90 mph on the freaking gun. How I wish the Reds would have given us Chapman, although then we wouldn't have Fiers and Gomez. We have to get a decent lefty.
As for the other free agents and options out there, I just don't think you want to invest that much into Heyward or Chris Davis. Both are going to bring HUGE money. Davis is a basepath killer. Love Heyward on this team, but he is going to get 180 million.