I too try to keep to the 5K increments, but as Nuclearslurpee said, specialization is key. Both my Frigates and Destroyers or 10KT, however Frigates are "attack" vessles while Destroyers are "defensive" vessels.
Example my "Aegis Fate" class Frigate
Aegis Fate class Heavy Frigate 9,944 tons 293 Crew 2,003.2 BP TCS 199 TH 1,632 EM 750
8206 km/s Armour 5-41 Shields 25-375 HTK 64 Sensors 0/0/0/0 DCR 4 PPV 38.88
Maint Life 2.42 Years MSP 1,503 AFR 198% IFR 2.7% 1YR 352 5YR 5,274 Max Repair 408 MSP
Cryogenic Berths 200
Commander Control Rating 3 BRG AUX CIC
Intended Deployment Time: 12 months Morale Check Required
M34-E816 MPD (2) Power 1632 Fuel Use 89.67% Signature 816 Explosion 15%
Fuel Capacity 1,000,000 Litres Range 20.2 billion km (28 days at full power)
Class 10-D Shield Array (1) Recharge Time 375 seconds (0.1 per second)
Series 1 MAC A16M1 (1) Range 256,000km TS: 8,206 km/s Power 16-4 RM 40,000 km ROF 20
Twin 4.7" Naval Coilgun Turret (2x2) Range 160,000km TS: 12000 km/s Power 8-8 RM 40,000 km ROF 5
Quad Gauss A4-17M1 Turret (2x16) Range 10,000km TS: 16000 km/s Power 0-0 RM 10,000 km ROF 5
MAC FC R256-TS8.4k (1) Max Range: 256,000 km TS: 8,400 km/s 96 92 88 84 80 77 73 69 65 61
Coilgun BFC 256-12k (1) Max Range: 256,000 km TS: 12,000 km/s 96 92 88 84 80 77 73 69 65 61
PD BFC R64-TS16k (1) Max Range: 64,000 km TS: 16,000 km/s 84 69 53 38 22 6 0 0 0 0
SFR-10 (2) Total Power Output 20.1 Exp 5%
AS1-R1 (1) GPS 2 Range 1.7m km MCR 157.3k km Resolution 1
ECM 10
This design is classed as a Military Vessel for maintenance purposes
This design is classed as a c for auto-assignment purposes
and my "Gatling" class Destroyer
Gatling class Destroyer 9,807 tons 261 Crew 1,906.8 BP TCS 196 TH 1,632 EM 750
8320 km/s Armour 5-40 Shields 25-375 HTK 69 Sensors 0/0/0/0 DCR 4 PPV 39.68
Maint Life 2.48 Years MSP 1,486 AFR 192% IFR 2.7% 1YR 334 5YR 5,015 Max Repair 408 MSP
Cryogenic Berths 200
Commander Control Rating 3 BRG AUX CIC
Intended Deployment Time: 12 months Morale Check Required
M34-E816 MPD (2) Power 1632 Fuel Use 89.67% Signature 816 Explosion 15%
Fuel Capacity 1,000,000 Litres Range 20.5 billion km (28 days at full power)
Class 10-D Shield Array (1) Recharge Time 375 seconds (0.1 per second)
Series 1 MAC A16M1 (1) Range 256,000km TS: 8,320 km/s Power 16-4 RM 40,000 km ROF 20
Quad Gauss A4-17M1 Turret (6x16) Range 10,000km TS: 16000 km/s Power 0-0 RM 10,000 km ROF 5
PD BFC R64-TS16k (2) Max Range: 64,000 km TS: 16,000 km/s 84 69 53 38 22 6 0 0 0 0
MAC FC R256-TS8.4k (1) Max Range: 256,000 km TS: 8,400 km/s 96 92 88 84 80 77 73 69 65 61
SFR-5 (1) Total Power Output 5 Exp 5%
AS1-R1 (1) GPS 2 Range 1.7m km MCR 157.3k km Resolution 1
AS51-R100 (1) GPS 6400 Range 51.3m km Resolution 100
ECM 10
This design is classed as a Military Vessel for maintenance purposes
This design is classed as a c for auto-assignment purposes
Note that both have Gauss PD turrets and an Anti-Ship spinal laser. Next campaign i'll be changing my design philosophy a little and have frigates be 10-15% faster then Destroyers and Cruisers.
I would also recommend a dedicated Scout/Recon destroyer for your fleets.
My 'Raven' class Scout Destroyer
Raven class Scout Destroyer 9,987 tons 259 Crew 1,926.2 BP TCS 200 TH 1,632 EM 750
8171 km/s Armour 5-41 Shields 25-375 HTK 62 Sensors 0/0/0/0 DCR 4 PPV 29.12
Maint Life 2.41 Years MSP 1,482 AFR 199% IFR 2.8% 1YR 350 5YR 5,244 Max Repair 408 MSP
Hangar Deck Capacity 500 tons
Commander Control Rating 3 BRG AUX CIC
Intended Deployment Time: 12 months Flight Crew Berths 10 Morale Check Required
M34-E816 MPD (2) Power 1632 Fuel Use 89.67% Signature 816 Explosion 15%
Fuel Capacity 1,000,000 Litres Range 20.1 billion km (28 days at full power)
Class 10-D Shield Array (1) Recharge Time 375 seconds (0.1 per second)
Series 1 MAC A16M1 (1) Range 256,000km TS: 8,171 km/s Power 16-4 RM 40,000 km ROF 20
Quad Gauss A4-17M1 Turret (4x16) Range 10,000km TS: 16000 km/s Power 0-0 RM 10,000 km ROF 5
PD BFC R64-TS16k (1) Max Range: 64,000 km TS: 16,000 km/s 84 69 53 38 22 6 0 0 0 0
MAC FC R256-TS8.4k (1) Max Range: 256,000 km TS: 8,400 km/s 96 92 88 84 80 77 73 69 65 61
SFR-5 (1) Total Power Output 5 Exp 5%
AS1-R1 (1) GPS 2 Range 1.7m km MCR 157.3k km Resolution 1
LongR AS81-R100 (1) GPS 16000 Range 81.1m km Resolution 100
ECM 10
Strike Group
1x Cat's Eye Recon Fighter Speed: 12038 km/s Size: 9.83
Recon fighter:
Cat's Eye class Recon Fighter 492 tons 18 Crew 168.9 BP TCS 10 TH 59 EM 0
12038 km/s Armour 1-5 Shields 0-0 HTK 3 Sensors 0/6/0/0 DCR 0 PPV 0
Maint Life 1.64 Years MSP 21 AFR 19% IFR 0.3% 1YR 9 5YR 138 Max Repair 88.8 MSP
Lieutenant Control Rating 1
Intended Deployment Time: 3 days Morale Check Required
R3.7-E118 MPD (1) Power 118.4 Fuel Use 557.99% Signature 59.20 Explosion 20%
Fuel Capacity 14,000 Litres Range 0.92 billion km (21 hours at full power)
AS51-R100 (1) GPS 6400 Range 51.3m km Resolution 100
EM1-6 (1) Sensitivity 6 Detect Sig Strength 1000: 19.4m km
This design is classed as a Fighter for production, combat and planetary interaction
This design is classed as a a for auto-assignment purposes
IF you are going to go with Frigate & Destroyer leader class vessels you might consider making those your jump ships for the squadron. I would advise against combining your jump ship with your scout ship/ship with large actives, since that would be a primary target.