PPC ad groups and budget question

Hello everyone,

newbie here, so i hope my questions are not too stupid.

I just finished my Ads learning courses and i am in the planning mode of my first Adwords campaign.

My first problem is segmenting my ad groups, i don't know weather i should segment them according to types or similar searches.

Specifically, i am planning on selling mobility scooters.

Should i divide them into following ad groups:
-3 wheel mobility scooters
-4 wheel mobility scooters
-Heavy duty mobility scooters
-Lightweight mobility scooters

Or should i divide them according to similar searches:
-Mobility scooters
-Senior scooters
-Handicap scooters
-Power scooters
-Disability scooters

My campaign template currently includes the similar searches ad groups, 5 ad groups total with an average of 5 keywords/adgroup and 4 different adcopies/ad group.


My second problem is planning the financial part of my campaign. Since my avg. PPC is around 1.5$, i am worried about my 300-400$/month budget.
I am trying to decide which strategy would be the best:

1. Should i include only the most specific keywords that are at least expected to get a higher conversion rate and then gradually broaden my search?
2. Should i start the campaign with lower budget -150$/month, just to get data, that will give me some level of insight into the performance of my ads and then focus only on the best performing keywords and increase the budget?

If anyone has an alternative strategy suggestions i will be happy to hear them, like i said i am a complete beginner in adwords.

I am trying to understand which way will give me best results without wasting too much time and money, because i assume that if i do enough research before the actual campaign start i can avoid some unwanted results...