I usually don't even begin considering that sort of effort until I'm at around the mid-AM stage of power and propulsion.
Kinda strange in this latest game: almost my entire military force consists of FACs. I've got a quartet of frigates that are close to a decade out of date, a pair of heavy cruisers that have been stuck in a system for close to 15 years while my JGC is refitted (and which are practically falling apart), and 22 FACs (8 MII, 14 MI). Of course, I'm screwed if anything serious shows up, as those were mainly built to keep the colonists from screaming while I waited twenty years to get decent missile and sensor researchers. I mean damn, I'm 24 years in, I'm still at AS strength-36, but I have internal confinement drives.
Templar II class Frigate 10,200 tons 1080 Crew 2128.6 BP TCS 204 TH 1056 EM 0
5176 km/s Armour 3-41 Shields 0-0 Sensors 80/1/0/0 Damage Control Rating 15 PPV 49.2
Maint Life 2.49 Years MSP 652 AFR 166% IFR 2.3% 1YR 146 5YR 2192 Max Repair 280 MSP
Magneto-plasma Drive E7.2 (12) Power 88 Fuel Use 72% Signature 88 Armour 0 Exp 10%
Fuel Capacity 400,000 Litres Range 98.0 billion km (219 days at full power)
Twin 15cm C5 Ultraviolet Laser Turret (2x2) Range 192,000km TS: 10000 km/s Power 12-10 RM 4 ROF 10 6 6 6 6 4 4 3 3 2 2
Quad 10cm C3 Ultraviolet Laser Turret (2x4) Range 120,000km TS: 10000 km/s Power 12-12 RM 4 ROF 5 3 3 3 3 2 2 1 1 1 1
Fire Control S16 96-12000 (1) Max Range: 192,000 km TS: 12000 km/s 95 90 84 79 74 69 64 58 53 48
Fire Control S12 72-12000 (1) Max Range: 144,000 km TS: 12000 km/s 93 86 79 72 65 58 51 44 37 31
Stellarator Fusion Reactor Technology PB-1 (1) Total Power Output 48 Armour 0 Exp 5%
Active Search Sensor MR100-R20 (1) GPS 5600 Range 100.2m km Resolution 20
Active Search Sensor MR2-R1 (1) GPS 28 Range 2.2m km Resolution 1
Thermal Sensor TH10-80 (1) Sensitivity 80 Detect Sig Strength 1000: 80m km
This design is classed as a Military Vessel for maintenance purposes
Templar III class Frigate 5,750 tons 570 Crew 1649.7 BP TCS 115 TH 1150 EM 360
10000 km/s Armour 3-28 Shields 12-300 Sensors 48/1/0/0 Damage Control Rating 2 PPV 16
Maint Life 2.34 Years MSP 359 AFR 132% IFR 1.8% 1YR 90 5YR 1343 Max Repair 173 MSP
Internal Confinement Fusion Drive E6.5 (10) Power 115 Fuel Use 65% Signature 115 Armour 0 Exp 12%
Fuel Capacity 230,000 Litres Range 110.8 billion km (128 days at full power)
Delta R300/12.5 Shields (5) Total Fuel Cost 63 Litres per day
20cm C1.5 Far Ultraviolet Laser (4) Range 256,000km TS: 10000 km/s Power 10-1.5 RM 5 ROF 35 10 10 10 10 10 8 7 6 5 5
Fire Control S12 128-9000 (1) Max Range: 256,000 km TS: 9000 km/s 96 92 88 84 80 77 73 69 65 61
Tokamak Fusion Reactor Technology PB-1 (2) Total Power Output 8 Armour 0 Exp 5%
Active Search Sensor MR15-R1 (1) GPS 144 Range 15.8m km Resolution 1
Active Search Sensor MR100-R40 (1) GPS 5760 Range 100.2m km Resolution 40
Thermal Sensor TH6-48 (1) Sensitivity 48 Detect Sig Strength 1000: 48m km
This design is classed as a Military Vessel for maintenance purposes
Lesson learned. Screw PD, build 'em fast and expendable.