1. Preparing
First thing first, you need to prep vehicles for the suits. Vehicles in their current state are not ready for the introduction of pilot suits.

A Compelling Reason
There needs to be a compelling reasons to use these suits over HMG Heavies when piloting, without the suits making vehicles OP...

Add a small input delay to all vehicle controls.
A 0.075s delay to everything. Module activation. Acceleration. Turret manipulation. Turning. Brakes. Everything.
The purpose of this is to make vehicles feel clumsy and a little unwieldy without a pilot suit. Pilot Dropsuit will completely negate this input delay. This is the compelling reason to use a fragile pilot suit instead of just another HMG Heavy.

Vehicle Parity
We need the full lineup of HAVs, LAVs, DSs, and Turrets if we want pilot suits to make any sense. This means adding a lot of Minmatar and Amarr stuff.

2. Numbers
The itty gritty.
Spreadsheeeeeeeeet!

Base Stats
I actually took a lot of inspiration from the Capsules in EVE when making my spreadsheet. For people that don't know, Capsules in EVE are essentially pilot to ship interfaces, that also double as ships/escape pods.
They are the lore behind why one person can control a whole Battleship and all of its subsystems practically by themself.
Very cool and high tech little things.

They are also completely defenseless, cannot be modded, and have no armamants to speak of. But they are fast. They are meant to escape from combat. Escape pods.

So, the Pilot suits in my spreadsheet are extremely squishy, only carry a single sidearm, have no module slots, and are really really fast. An Amarr Pilot would make a Minsout go green with envy.
By having the fastest base movement speed in the game, less than 100 HP, and only a sidearm, retreat will be their only option in suitVsuit combat.
They also have equipment slots in the higher tiers. These are intended for things like repair tools and potentially even uplinks if a LAV specialist wants to deploy some uplinks really far away.

Something's I didn't include were regen rates, shield delays, melee, and stamina stats. All of those things but stamina should be subpar. Its just for running away.

Bonuses
These suits need to be worthwhile to use and spec into for any vehicle user. Not just HAVs. Not just LAVs. Not Just Dropships. Their bonuses need to be pretty unspecialized and really just follow a general racial theme because of this. Real generalist bonuses that anyone can work with at least a little bit.
I took a little inspiration from both Assault and Sentinel suits when tailoring the bonuses to each race, since they both have racially appropriate and fairly unspecialized bonuses.

3. Colors!
The most important part. Period.

Personally, I'd like to see them be colored blaze orange and white, like these guys.
Just imagine a Minscout with a color scheme like that. That would look cool.
But I'd also like to see what suggestions other people have. Remember that they can't be colored like another role. So they are pretty restricted as far as choices go.