If he's available in one of those rare leagues without farm systems or reserve lists, Marte is an obvious buy. His ceiling is probably as a 20/30 guy, though I don't expect that out of him right away (and keep in mind I'm talking long-term, best case scenario). His 847 OPS at AAA might sound unimpressive, but it puts Marte in the Top 10 among qualifiers in the International League. I think there might be an adjustment period for Marte where he whiffs too much and the BA is low, but the power and speed should be there and he'll play every day. Most of the trade rumors I've seen involve talent moving from the N.L. to the A.L., so Marte could be worth blowing most or all of your remaining FAAB depending on your needs.
As far as who sits for Marte, I'd imagine it would be some combination of Casey McGehee and Alex Presley, with Garret Jones slotting in at either left field or first base depending on who sits. Jones will probably sit against some lefties in this arrangement.
Is Donovan Solano worth picking up? In N.L.-only, sure. Unlike with Marte, though, the upside is extremely limited. Solano's minor league profile is more of organizational filler than future star, and while his current Major League numbers are enticing, Solano has a 633 OPS across 2795 minor league plate appearances. Add to this a lack of any discernible power or speed and Solano looks more like AAA lifer than late career surprise. Solano might get a good chunk of AB at 3B, but I don't expect him to keep playing at this clip. Pick him up if your roster has a dead spot, but in carryover leagues your roster shouldn't have any dead spots at this point.