Nothing wrong working the body cosmetics but keep in mind a few things. 1) You will be heavier, 2) it will effect your ability to recover and hence your ability to train aerobically 3) there is no real transference to aerobic performance.
You can train both concurrently but both will be compromised to the effectiveness yielded. And you'll need to eat a lot to keep yourself from an overtrained state. Depending on the intensity of the efforts with the weights stress to the CNS would be a strong consideration.
Also why 5x5? If you haven't been on the weights for a while then this is a lot of volume. Try more along the lines of 3 sets of 5 reps and just follow a linear progression (start with an empty or near empty bar and add weight each session). Make sure you squat right and also and add deadlifts if you weren't doing them already. And FWIW I never, ever do "biceps" or "triceps".
As for the efforts, a "tad over FTP" would be along the lines of 101-105%. You can go to 110% but it will be shorter duration (~3mins). As cyco mentioned velodrome work is very good for ultra intense efforts.
Thanks a million. Funny you should say the thing about recovery as I was thinking the exact same thing yesterday when I was out riding. I'll probably switch to something like this next week:
Monday: Weight training
Tuesday: Bike ride 1,5-2 hours at a tad over FTP
Wednesday: Bike ride - maybe a short ride with low intensity/Day off/Swimming
Thursday: Bike ride 1,5-2 hours at a tad over FTP
Friday: Weight training
Saturday: Day off
Sunday: Bike ride 2-3 hours
Knowing how my winter usually is, there will be a lot of changes and missed sessions, so it's just for reference.
Weight training - I know I will gain weight, and I'll probably change my routine so it will include less exercises and focusing on musclegroups that are relevant for cycling, and then from time to time just do a simple pushup or pull up to make sure I still look good in the mirror. I'm thinking of a routine similar to this:
Warmup - 10 minutes xtrainer, row machine or stationary bike
Squat - probably 4x4
Face pulls/Stability row
Cool down - same as warmup