Do you have trees on your postage property? A tree limb 18-23' AGL is fitting for a nearly invisible I-Vee antenna. I say 23' to accommodate the 5' vertical depth of the I-Vee; therefore, the entire antenna is 1/2λ AGL. Your choice of 20w will work splendidly for 16 AWG wire or up to 12 AWG I-Vee antenna. The only need for 12 AWG in the case of 25W output would be strength against storm winds.
Hang it from the limb using a small single pulley attached to end of throw line.
Though the pulley run a seconding line to raise and lower the antenna as needed.
A 90 or 106 degree I-Vee will be about 5' in the vertical height above your leg spreader. A 90d I-V will have a leg spread just shy of 12', while a 106d spread will be 13.18'. Leg spreader may be 1/2"D wooden dowel section with 1/2"I.D. pipe segment (copper) connectors. Or 1/2" camo painted PVC with single or multiple segment connectors. Use 550 paracord strung from ends of spreader to ground weights, I use repurposed brake rotors, to tether antenna against Colorado winds. The center fed coax dangles perpendicular to spreader center and affixed to spreader to insure no sag; also eliminates coax weight on connector.
A choke balun of the usual "Fugly" nature will be far more conspicuous than a 1:1
http://www.vk3bq.com/2014/09/24/11-current-balun/ current balun made in the manner shown. In the referenced build the author uses coax. Coax is not necessary. A 48" of repurposed extension cord is usable; just keep track of + and - strands; mark the ends.
Tested my I-Vee yesterday with and without the 1:1 balun with the leg ends < 10' AGL. Supposedly at this height the need is NIL.
Without: 1.5W dead key 1.05:1 swinging to 13W and 1.15:1.
With: 1:1, 1.5W swinging 13W.
I might add, the 1:1 balun is wound with 16 AWG magnet wire chassis rated for 100W continuous; at 13.7 VDC. I have been using it and modulating, very briefly, upwards of 1200W without smoking it.
Build a 1:1 balun with FT240-43 with dual strands at 7 wraps each direction. Mount within 3D printer made PETG frame having nearly the height of an
SO-239, with the length and width minimally necessary to frame the wound toroid, mounted SO-239, connectors to affix antenna legs, and a small eye-bolt to hang it with. 100mm L x 75mm W x 25mm H. Frame is open to the weather across the broadsides.
I don't believe you need concern yourself with RFI and the neighbor's radios with 25W of RF power. As I understand it, your coax is the radiating entity that emits the RFI that may cause interference. Your coax with a low or balance SWR should not cause a problem. A choke's purpose is to minimize if not eliminate any that may occur.