With Lucas there are a couple ways to get shield pressure started. The most basic is to approach after chucking Ice from a Double Jump Cancel, you can follow the PK Freeze a good distance before it's gone, just follow a few basic rules: Don't approach the same way, mix up using PK Freeze again, running up too them, and shorthopping, likewise switch up what you do, that is to say, don't always do Fair after following it (This is assuming they don't get hit/shield it) Once you start to get closer more options are available TO you.
From closer range DJC Fair and Short Hop/Running Magnet are excellent, safe ways to get pressure started. For example, if you jump at someone and start magnet and they try to jump to avoid your attack, you can jump after them and choose the correct move to deal with their option. If you actually touch their shield with your Magnet then you can get shield pressure going. With Fair (and other aerials if you use them correctly) it's all a matter of making sure you've got your DJCs down and your spacing correct. Another important element of doing this is, if you ARE hitting their shield with an aerials it's important that you select an aerial that will let you end up BEHIND someone's shield. Once you're in someone's face, if they're ALREADY holding their shield up, it's best to go for Magnet pressure as it's your safest bet.
As far as Doubles go, I haven't played him a whole lot, but he's probably got some nice things going for him. Obviously being able to heal off a partner's projectile/energy based moves would useful, he has fast and weak moves that could be used to save partners (Uair, Magnet, Sourspot Fair), and good followup moves in Bair and any of his OU Smash attacks. I'd take this advice with a grain of salt and/or wait for better, but it'd be worth giving a shot hitting up the lab and testing some stuff out. It's just what comes to mind immediately for me.